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UNIVERSITY OF CALIFORNIA AT LOS ANGELES

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I'OLUME ONE

A DICTIONARY OF

E LECTRIC AL

WORDS, TERMS and PHRASES

BY

EDWIN J. HOUSTON, A.M., PH.D.

EMERITUS PROFESSOR OF NATURAL PHILOSOPHY AND PHYSICAL GEOGRAPHY

IN THE CENTRAL HIGH SCHOOL OF PHILADELPHIA J PROFESSOR OF

PHYSICS IN THE FRANKLIN INSTITUTE OF PENNSYLVANIA ;

ELECTRICIAN OF THE INTERNATIONAL ELECTRICAL

EXHIBITION, ETC., ETC., ETC.

P ART ONE — A to S

NEW YORK P. F. COLLIER fcf SON

1902

COPYRIGHT 1889, 1892, 1894, 1897 Bv THE W. J. JOHNSTON COMPANY

APPENDIX B

COPYRIGHT 1897

BY EDWIN J. HOUSTON

S05T WtflcL

PREFACE TO THE FIRST EDITION.

THE rapid growth of electrical science, and the almost daily addition to it of new words, terms and phrases, coined, as they too frequently are, in ignorance of those already existing, have led to the production of an electrical vocabulary that is already bewildering in its extent. This multiplicity of words is extremely discourag- ing to the student, and acts as a serious obstacle to a general dissemination of elec- trical knowledge, for the following reasons :

1. Because, in general, these new terms are not to be found eve^ in the unabridged editions of dictionaries.

2. The books or magazines, in which they were first jroposed, are either inac- cessible to the ordinary reader, or, if accessible, are often written in phraseology un- intelligible except to the expert.

3. The same terms are used by different writers in conflicting senses.

4. The same terms are used with entirely different meanings.

5. Nearly all the explanations in the technical dictionaries are extremely brief as regards the words, terms and phrases of the rapidly growing and comparatively new science of electricity.

In this era of extended newspaper and periodical publication, new words are often coined, although others, already in existence, are far better suited to express the same ideas. The new terms are used for a while and then abandoned ; or, if retained, having been imperfectly defined, their exact meaning is capable of no little ambiguity; and, subsequently, they are often unfortunately adopted by^different writers with such varying shades of meaning, that it is difficult to understand their true and exact significance.

Then again, old terms buried away many decades ago and long since forgotten, are \ dug up and presented in such new garb that their creators would most certainly fail to recognize them.

It has been with a hope of removing these difficulties to some extent that the author r has ventured to present this Dictionary of Electrical Words, Terms and Phrases to his ^$ brother electricians and the public generally.

He trusts that this dictionary will be of use to electricians, not only by showing the sjt wonderful extent and richness of the vocabulary of the science, but also by giving the eral consensus of opinion as to the significance of its different words, terms or phrases. It is, however, to the general public, to whom it is not only a matter of interest but also one of necessity to fully understand the exact meaning of electrical literature, that the author believes the book will be of the greatest value.

In order to leave no doubt concerning the precise meaning of the words, terms and phrases thus defined, the following plan has been adopted of giving : (i.) A concise definition of the word, term or phrase.

(2.) A brief statement of the principles of the science involved in the definition. J— VOL. 1

853927

(3.) Where possible and advisable, a cut of the apparatus described or employed in connection with the word, term or phrase denned.

It will be noticed that the second item of the plan makes the Dictionary ap- proach to some extent the nature of an Encyclopedia. It differs, however, from an Encyclopedia in its scope, as well as in the fact that its definitions in all cases ' are concise.

Considerable labor has been expended in the collection of the vocabulary, for which purpose electrical literature generally has been explored. In the alphabetical arrangement of the terms and phrases defined, much perplexity has arisen as to the proper catch-word under which to place them. It is believed that part of the difficulty in this respect has been avoided by the free use of cross references.

In elucidating the exact meaning of terms by a brief statement of the principles of the science involved therein, the author has freely referred to standard textbooks on electricity, and to periodical literature generally. He is especially indebted to works or treatises by the following authors, viz. : S. P. Thompson, Larden, Gumming, Hering, Prescott, Ayrton, Ayrton and Perry, Pope, Lockwood, Sir William Thom- son, Fleming, Martin and Wetzler, Preece, Preece and Sivewright, Forbes, Max- well, De Watteville, J. T. Sprague, Culley, Mascart and Joubert, Schwendler, Fontaine, Noad, Smee, Depretz, De la Rive, Harris, Franklin, Cavallo, Grove, Hare, Daniell, Faraday and very many others.

The author offers his Dictionary to his fellow electricians as a starting point only. He does not doubt that his book will be found to contain many inaccuracies, ambig- uous statements, and possibly doubtful definitions. Pioneer work of this character must, almost of necessity, be marked by incompleteness. He, therefore, invites the friendly criticisms of electricians generally, as to errors of omission and commis- sion, hoping in this way to be able finally to crystallize a complete vocabulary of electrical words, terms and phrases.

The author desires in conclusion to acknowledge his indebtedness to his friends, Mr. Carl Henng, Mr. Joseph Wetzler and Mr. T. C. Martin, for critical exami- nation of the proof sheets ; to Dr. G. G. Faught for examination of the proofs of the parts relating to the medical applications of electricity, and to Mr. C. E. Stump for valuable aid in the illustration of the book ; also to Mr. George D. Fowle, Engineer of Signals of the Pennsylvania Railroad Company, for information concern- ing their System of Block Signaling, and to many others.

EDWIN J. HOUSTON.

» CENTRAL HIGH SCHOOL, PHILADELPHIA, PA., SEPTEMBER, 1889.

PREFACE TO THE SECOND EDITION.

THE first edition of the "Dictionary of Electrical Words, Terms and Phrases" met with so favorable a reception that the entire issue was soon exhausted. Although but a comparatively short time has elapsed since its publication, electrical progress has been so marked, and so many new words, terms and phrases have been introduced into the electrical nomenclature, that the preparation of a new edition has been determined on rather than a mere reprint from the old plates.

The wonderful growth of electrical science may be judged from the fact that the present work contains more than double the matter and about twice the number of definitions that appeared in the earlier work. Although some of this increase has been due to words which should have been in the first edition, yet in greater part it has resulted from an actual multiplication of the words used in electrical literature.

To a certain extent this increase has been warranted either by new applications of electricity or by the discovery of new principles of the science. In some cases, how- ever, new words, terms or phrases have been introduced notwithstanding the fact that other words, terms or phrases were already in general use to express the same ideas.

The character of the work is necessarily encyclopedic. The definitions are given in the most concise language. In order, however, to render these definitions intel- ligible, considerable explanatory matter has been added.

The Dictionary has been practically rewritten, and is now, in reality, a new book based on the general lines of the old book, but considerably changed as to order of arrangement and, to some extent, as to method of treatment.

As expressed in its preface, the author appreciates the fact that the earlier book was tentative and incomplete. Though the wide scope of the second edition, the vast number of details included therein, and the continued growth of the electrical vocabulary must also necessarily make this edition incomplete, yet the author ventures to hope that it is less incomplete than the first edition. He again asks kindly criti- cisms to aid him in making any subsequent edition more nearly what a dictionary of so important a science should be.

The order of arrangement in the first edition has been considerably changed. The initial letter under which the term or phrase is defined is in all caSjes that of the noun.

For example, "Electric Light " is defined under the term " Light, Electric " ;

" Diameter of Commutation " under "Commutation, Diameter of , " "Alter- nating Current Dynamo- Electric Machine" under "Machine, Dynamo-Electric, Alternating Current ." As before, the book has numerous cross references.

Although the arrangement of the words, terms and phrases under the initial letter of the first word, term or phrase, as, for example, " Electric Light" under the letter E, might possess some advantages, yet, in the opinion of the author, the educational value

of the work would be thereby considerably decreased, since to a great extent such an arrangement would bring together incongruous portions of the science.

Frequent cross references render it possible to use the Dictionary as a text-book in connection with lectures in colleges and universities. With such a book the student need nuke notes only of the words, terms or phrases used, and afterwards, by the use of the definitions and explanatory matter connected therewith, work up the general subject matter of the lecture. The author has successfully used this method in his teaching.

In order to separate the definitions from the descriptive matter, two sizes of type have been used, the definitions being placed in the larger sized type.

In the descriptive matter the author has not hesitated to quote freely from standard electrical works, electrical magazines, and periodical literature generally. Among the numerous works consulted, besides those to which reference has already been made in the preface to the first edition, he desires to acknowledge his indebtedness espe- cially to "The Alternating Current Transformer," by J. A. Fleming ; to various works of John W. Urquhart ; to "Modern Views of Electricity," by Prof. O. J. Lodge; to "A Text-book of Human Physiology," by Landois & Sterling; and to "Practical Application of Electricity in Medicine and Surgery, " by Liebig & Rohe.

The cuts or diagrams used in the book have either been drawn especially for the work or have been taken from standard electrical publications.

The chart of standard electrical symbols and diagrams has been taken from Prof. F. B. Crocker's paper on that subject.

The definition of terms used in systems of electric railways have been taken mainly from a paper on " Standards in Electric Railway Practice," by O. T. Crosby.

The author desires especially to express his obligations to Prof. F. B. Crocker of the Electrical Engineering Department, Columbia College, New York, and to Carl Hering, of Philadelphia, for critical examination of the entire manuscript and for many valuable suggestions ; also to The Electrical World and the Electrical Engineer of New York, and to Prof. Elihu Thomson, Edward Caldwell, T. C. Martin, Dr. Louis Bell, Joseph Wetzler, Nikola Tesla, Wm. H. Wahl, Prof. Wm. D. Marks, Prof. A. E. Dolbear, C. W. Pike, John Hoskin, and numerous others, for aid in connection with new words or phrases. So far as they relate to the medical applications of electricity, the proof sheets were revised by Dr. G. G. Faught, of Philadelphia.

The author desires to thank critics of the first edition and the electrical fraternity in general for valuable suggestions. He presents this second e lition of his Dictionary in the hope that it may to some extent properly represent the vocabulary of electrical science.

CENTRAL HIGH SCHOOL, EDWIN J. HOUSTON.

PHILADELPHIA, May, 1892.

PREFACE TO THE THIRD EDITION.

THE second edition of the "Dictionary of Electrical Words, Terms, and Phrases" was exhausted in such a comparatively short time that the publishers believed that what new matter might be required for a third edition could best be added in the form of an appendix.

Although not quite two years have elapsed since the issue of the second edition, yet the growth of electrical science has continued at so rapid a pace, and new words, terms, and phrases have of necessity been introduced so rapidly, that fully twenty per cent., both of new words and new matter, have been found necessary for the third edition. Had this fact been known in time, it might have been better to have developed the additional matter throughout the text, rather than placing it at the end of the book as an appendix.

Should a demand be made for a fourth edition, the author contemplates re- writing and re-arranging the entire volume. He is thoroughly aware of the inaccuracies and incompleteness of many of the definitions in the second edition, and hopes, in the event of a demand for a fourth edition, to produce a volume more nearly ap- proximating to what an electrical dictionary should be. In the meantime, he again asks the kindly criticisms of his fellow laborers in the electrical field to aid him in the work.

In order to facilitate the use of the cross-references, all words, terms, and phrases referred to in the appendix are so marked; i. e., (See Appendix — Insulation, Kilo- metric, of Cable. ) All references not so marked will be found in the main text of the dictionary.

The author desires to express his obligations to numerous authors and technical journals for information as to new words, terms, and phrases, and to the significance generally given to them in actual use. He desires especially to acknowledge his obligations to his colleague, Mr. A. E. Kennelly, and to Professors R. A. Fessenden, C. Wellman Park; to Messrs. C. P. Steinmetz, J. F. Kelly, O. B. Shallenberger, Carl Hering, H. W. Frye, W. D. Weaver, W. F. C. Hasson, Townsend Wolcott, J. B. Cahoon, and many others, for reading of proof sheets and suggestions.

The author presents this third edition of the Dictionary with the hope that it may prove of value to the electrical fraternity.

EDWIN J. HOUSTON. PHILADELPHIA, May, 1894.

PREFACE TO THE FOURTH EDITION.

TN preparing the fourth edition of his " Dictionary of Electrical 1 Words, Terms and Phrases," the author soon found that the recent marvellous growth in the electrical vocabulary was such that it would be impossible to add, in the shape of a separate appendix, the new words, terms and phrases only, that it was necessary to introduce into the book. This will be evident from the fact that the added words exceed in number those already contained in the first, second and third editions. Since it was deemed inadvisable by the publisher to recast the entire book, the only course left open to the author was to alphabetically arrange all the old and new words, and to present them in concise definitions without any ency- clopaedic matter, referring the reader to the matter contained in the earlier editions for illustration and detail.

It has also been thought advisable to introduce a change in the manner of arrangement, the words, terms and phrases being alpha- betically arranged according, either to the word, or to the first word of the term or phrase. This has permitted the entire suppression of all cross references, which, in view of the author's past expe- rience, he believes will prove an advantage.

The author desires to acknowledge the very valuable assistance afforded him by his colleague, Dr. A. E. Kennelly, in the prepa- ration of the matter for the fourth edition, both in collecting new terms, as well as in preparing the definitions, and reading the proof.

The author trusts, that the fourth edition of his electrical Diction- ary will prove of benefit not only to the electrical world but to the reading public generally.

All criticisms will be gladly received.

EDWIN J. HOUSTON.

PHILADELPHIA, December, 1897.

A DICTIONARY

OF

ELECTRICAL

WORDS, TERMS AND PHRASES.

A. or An. — An abbreviation sometimes used in medical electricity for anode. (See Anode.)

A. C. C. — An abbreviation used in medical electricity for Anodic Closure Contraction. (See Contraction, Anodic Closure.)

A. D. C. — An abbreviation used in medical electricity for Anodic Duration Contraction. (See Contraction, Anodic Duration)

A. 0. C. — An abbreviation used in medical electricity for Anodic Opening Contraction. (See Contraction, Anodic Opening.)

Abscissa of Rectilinear Co-ordinates. — A line or distance cut off along axis of abscissas.

The abscissa of the point D, Fig. i, on the curve O D R, is the distance D I, or its equal A 2, measured or cut off on the line A C, the axis of abscissas; or, briefly, A 2, is the abscissa of the point D.

Abscissas, Axis of — One of the

axes of co-ordinates used for determining the position of points on a curved line.

Thus the position of the point D, Fig. i, on the curved line O D R, is determined by the per- pendicular distances, D I and D 2, of such point from two straight lines, A B and A C, called the ax fs of co-ordinates. AC, A 2 C

is called the axis of ab- F*-r; **<**/ Co-ordinate*, scissas, and AB, the axis of ordinates. The point

A, where the lines are considered as starting or originating, is called fat point of origin, or, gen- erally, the origin.

The use of co-ordinates was first introduced by the famous mathematician, Des Cartes.

Absolute.— Complete in itself.

The terms absolute and relative are used in electricity in the same sense as ordinarily.

Thus, a galvanometer is said to be calibrated absolutely when the exact current strengths re- quired to produce given deflections are known ; or, in other words, when the absolute current strengths are known ; it is said to be calibrated relatively when only the relative current strengths required to produce given deflections are known.

The word absolute, as applied to the units em- ployed in electrical measurements, was introduced by Gauss to indicate the fact that the values of such units are independent both of the size of the instrument employed and of the value of gravity at the particular place where the instrument is used.

The word absolute is also used with reference to the fact that the values of the units could readily be redetermined from well known con- stants, in case of the loss of the standards.

The absolute units of length, mass, and time are more properly called the C. G. S. units, or the centimetre-gramme-second units. (See Units, Absolute.)

An absolute system of units based on the milli- gramme ^ millimetre, and second, was proposed by Weber, and was called the millimetre -milli- gramme-second units. It has been replaced by

Abs.]

[Ace.

the C. G. S. units. (See Units, Centimetre- Gramme- Second. Units, Fundamental.)

Absolute Block System for Railroads.—

(See Block System for Railroads, Absolute)

Absolute Calibration.— (See Calibration, Absolute)

Absolute Electrometer. — (See Electrome- ter, Absolute?)

Absolute Galvanometer. — (See Galva- nometer, Absolute?)

Absolute Unit of Current.— (See Current, Absolute Unit of.) •

Absolute Unit of Electromotive Force.— (See Force, Electromotive, Absolute Unit of.)

Absolute Unit of Inductance.— (See In- ductance, Absolute Unit of)

Absolute Unit of Resistance.— (See Re- sistance, Absolute Unit of)

Absolute Unit of Self-induction.— (See Induction, Self, Absolute Unit of)

Absolute Units.— (See Units, Absolute.)

Absolute Vacuum. — (See Vacuum, Ab- solute)

Absorption. — The taking, or, literally, drinking in, of one form of matter by another, such as a gas, vapor or liquid by a solid ; or of the energy of sound, light, heat, or elec- tricity by ordinary matter.

Absorption, Acoustic The taking

in of the energy of sound waves produced by one sounding or vibrating body by another vibrating body.

Acoustic absorption may result in the dissipa- tion of the absorbed energy, as heat, or in sym- pathetic vibrations. (See Vibrations, Sympathetic.)

Absorption, Electric The appar- ent soaking of an electric charge into the glass or other solid dielectric of a Leyden jar or condenser. (See Condenser.)

The capacity of a condenser varies with the time the condenser remains charged and with the time taken in charging. Some of the charge acts as if it soaked into the solid dielectric, and this is the cause of the residual charge. (See Charge, Residual.) Therefore, when the con-

denser is discharged, less electricity appears than was passed in ; hence the term electric absorption.

Absorption, Luminous The ab- sorption of the energy of light in its passage through bodies.

When sunlight falls on an opaque colored body, such for example as a red body, all the colors but the reds are absorbed. yThe reds are then thrown off and thus cause the color. In the same manner, when sunlight falls on a transparent colored body, such for example as red, all colors but the reds are absorbed, and the reds are transmitted.

When sunlight falls on a phosphorescent body, a part of the light is absorbed as heat ; another part is absorbed by the molecules being set into motion sufficiently rapid to cause them to emit light or to become luminous.

A mass of glowing gas or vapor absorbs waves of light of the same length as those it itself emits. This is the cause of the dark lines of the solar spectrum, called the Fraunhoffer lines.

The amount of light absorbed by the glass globe of an incandescent lamp, according to Urquhart, is as follows, viz.:

Clear glass 10 per cent.

Ground glass 35 "

Opalescent glass 50 "

Absorption, Selective The absorp- tion of a particular or selected character of waves of sound, light, heat, or electricity.

Absorption, Thermal The ab- sorption of heat energy in its passage through a body.

The phenomena of thermal absorption are similar to those of luminous absorption. A sub- stance that is transparent to heat, or which allpws heat waves to pass through without absorption, is called diathermanous, or diathermanic, or is said to be transparent to heat.

Absorptive Power. — (See Power, Absorp- tive)

Acceleration. — The rate of change of velocity.

Acceleration is thus distinguished from velocity: velocity expresses in time the rate- of- change of position, as a velocity of three metres per second ; acceleration expresses in time the rate-of-change of velocity, as an acceleration of one centimetre per second.

Since all matter is inert, and cannot change its

Ace.]

[Ace.

condition of rest or motion without the applica- tion of some force, acceleration is necessarily due to some force outside the matter itself. A force may therefore be measured by the acceleration it imparts to a given mass of matter.

Acceleration is positive when the velocity is in- creasing, and negative when it is decreasing.

Acceleration, Dimensions of The

value of the acceleration expressed in terms of the length or of distance by the time. (See Acceleration, Unit of.}

Acceleration, Unit of That ac- celeration which will give to a body unit- velocity in unit-time; as, for example, one centimetre-per-second in one second.

Bodies falling freely in a vacuum, and ap- proximately so in air, acquire an acceleration which in Paris or London, at the end of a second, amounts to about 981 centimetres per second, or nearly 32.2 ft. per second.

V A = — , or, in other words,

The acceleration equals the velocity divided by the time.

But, since velocity equals the Distance, or the

Length traversed in a Unit of Time, V = t .

L Therefore, A = X = -I. = ^ , Or

The acceleration equals the length, or the dis- tance passed through, divided by the square of the time in seconds.

These formulae represent the Dimensions of Acceleration.

Accumulated Electricity.— (See Electri- city, Accumulated^}

Accumulating1 Electricity. — (See Electri- city, Accumulating?)

Accumulation of Electricity.— (See Elec- tricity, Accumulation of.}

Accumulator. — A -word sometimes applied to any apparatus in which the strength of a current is increased by the motion past it of a conductor, the currents produced in which tend to strengthen and increase the current which causes the induction.

The word accumulator is sometimes applied to Sir Wm. Thomson's Electric Current Accumu- lator.

Current accumulators operate on the reaction principle of dynamo-electric machines. In this sense, therefore, a dynamo-electric machine is an accumulator. (See Machine, Dynamo-Electric, Reaction Principle of.}

Fig. 2. Barltrw's Whtel.

The copper disc D, Fig. 2, has freedom of rotation, on a horizontal axis at O, in a magnetic field, the lines of force of which, represented by the dotted lines in the drawing, pass downward perpendicularly into the plane of the paper.

If, now, a current from any source be passed in the direction A, O, B, C, A, through the circuit A, O, B, C, A, which is provided with spring contacts at O, and A, the disc will rotate in the direction of the curved arrow. This motion is due to the current acting on that part of the disc which lies between the two contacts — A and O. This apparatus is known as Barlow's Wheel.

If, when no current is passing through the circuit, the disc be turned in the direction of the arrow, a current is set up in such a direction as would oppose the rotation of the disc. (See Law, Lenz's.)

If, however, the disc be turned in the opposite direction to that of the arrow, induction currents will as before be produced in the circuit. As this rotation of the disc tends to move the circuit O A, towards the parallel but oppositely directed circuit B C, these two circuits being parallel and in opposite directions tend to repel one another, and there will thus be set up induced currents that tend to oppose the motion of rotation, and the current of the circuit will therefore increase in strength. (See Dynamics, Electro.} Should then a current be started in the circuit, and the original field be removed, the induction will be continued, and a current which, up to a certain extent, increases or accumulates, is maintained in the circuit during rotation of the disc. (Larden.)

Barlow's Wheel, when used in this manner, is known as Thomsons Electric Current Accumu- lator.

Acc.]

[Ace.

Accumulator. — A word often applied to a Leyden jar or condenser, which permits the gradual collection from an electric source of a greater charge than it would otherwise be capable of containing.

A condenser. (See Condenser?)

The ability of a source to accumulate an in- creased charge when connected to a condenser is due to the increased capacity which a plate or other conductor acquires when placed near another plate or conductor. (See Condenser. Jar, Leyden.}

Accumulator, Capacity of -- The

capacity of a condenser, expressed in micro- farads. (See Condenser, Capacity of.)

Accumulator or Condenser ; Laws of Ac- cumulation of Electricity.— Sir W. Snow Harris, by the use of his Unit-Jar and Elec- tric Thermometer, deduced the following laws for the accumulation of electricity, which we quote from Noad's " Student's Text-Book of Electricity," revised by Preece :

(l.) "Equal quantities of electricity are given off at each revolution of the plate of an electrical machine to an uncharged surface, or to a surface charged to any degree of saturation."

(2. ) "A coated surface receives equal quantities of electricity in equal times ; and the number of revolutions of the plate is a fair measure of the relative quantities of electricity, all other things remaining the same."

(3.) " The free action of an electrical accumula- tion is estimated by the interval it can break through, and is directly proportional to the quan- tity of electricity."

(4.) " The free action is inversely proportional to the surface."

(5.) " When the electricity and the surface are increased in the same ratio, the discharging in- terval remains the same ; but if, as the electricity is increased, the surface is diminished, the dis- charging interval is directly as the square of the quantity of electricity."

(6.) " The resistance of air to discharge is as the square of the density directly. "

According to some later investigations, the quantity a plane surface can receive under a given density depends on the linear boundary of the surface as well as on the area of the surface.

" The amount of electrical charge depends on

surface and linear extension conjointly. There exists in every plane surface what may be termed an electrical boundary, having an important rela- tion to the grouping or disposition of the electric particles in regard to each other and to surrounding matter. This boundary in circles or globes is represented by their circumferences. In plane rectangular surfaces, it is by their linear extension or perimeter. If this boundary be constant, their electrical charge varies with the square root of the surface. If the surface be constant the charge varies with the square root of the boundary. If the surface and boundary both vary, the charge varies with the square root of the surface multi- plied into the square root of the boundary."

These laws apply especially to continuous sur- faces taken as a whole, and not to surfaces divided into separate parts.

By electrical charge Harris meant the quantity sustained on a given surface under a given elec- trometer indication ; by electrical intensity, he meant the indication of the electrometer corre- sponding to a given quantity on a given surface.

(See Condenser, Capacity of. Capacity, Elec- trostatic. Capacity, Specific Inductive. )

Accumulators of this character are now generally called Condensers. (For more modern principles concerning their construction and capacity see Condenser. Condenser, Capacity of.)

Accumulator, Secondary or Storage Cell -- Two inert plates partially sur- rounded by a fluid incapable of acting cham- ically on either of them until after the passage of an electric current, when they become capable of furnishing an independent electric current.

This use of the term accumulator is the one most commonly employed. A better term for such a cell is a secondary or storage cell. (See Cell, Secondary or Storage.)

Commercially, an accumulator consists of a single jar and its electrolyte, in which a single set of positive and negative plates is properly placed.

Accumulator, Water-Dropping -- An apparatus devised by Sir W. Thomson for increasing the difference of potential between two electric charges.

The tube X Y, Fig. 3, connects with a reser- voir of water which is maintained at the zero potential of the earth. The water escapes from

Ach.]

the openings at C and D, in small drops and falls on funnels provided, as shown, to receive the separate drops and again discharge them.

The vessels A, A', and B, B', which are electrically connected as shown, are maintained at a certain small A hj difference of potential, as indicated by the respective -f- and — signs.

Under these c i r c u m - stances, therefore, C and D, A ' will be charged inductively FiS- 3- Water-Drop- with charges opposite to ting Acatmulator- those of A and B, or with — and -f- electricities respectively. As the drops of water fall on the funnels, the charges which the funnels thus con- stantly receive are given up to B' and A', before the water escapes. Since, therefore, B, B', and A, A', are receiving constant charges, the differ- ence of potential between them must continually increase. This apparatus operates on the same principle as the replenisher. The drops of water act as the carriers, and A, A', and B, B', as the hollow vessels. (See Replenisher.)

Achromatic. — Free from false coloration.

Images formed by ordinary lenses do not pos- sess the true colors of the object, unless the edges of the lenses are cut off by the use of a diaphragm ; i. f., an opaque plate with a central circular opening. The edges of the lenses disperse the light like an ordinary prism, and so produce rain- bow colored (prismatic) fringes in the image. The use of an achromatic lens is to obviate this false coloration.

Achromatizable. — Capable of being freed from false coloration.

Achromatize. — To free from false color- ation.

Achromatizing. — Freeing from false color- ation.

Acid, Spent A battery acid, or other

acid, that has become too weak for efficient action.

In a voltaic cell the acid of the electrolyte becomes spent by combining with the metal of the positive plate.

Acidometer. — A special form of hydrom- eter used in determining the specific gravity of the acid liquid in a secondary or storage

cell. (See Areometer or Hydrometer. Cell. Storage?)

The scale on the acidometer tube is made to in- dicate the density according to the distance the floating instrument sinks in the liquid.

Aclinic Line.— (See Line, Aclinic)

Acoustic Absorption. — (See Absorption, Acoustic?)

Acoustic Engraving. — (See Engraving, Acoustic?)

Acoustic Telegraphy. — (See Telegraphy, Acoustic?)

Acoustic Tetanus. — (See Tetanus, Acous- tic:)

Acoutemeter, Electric An ap- paratus for electrically testing the delicacy of hearing.

The Acoutemeter is one of the many applica- tions of Hughes' sonometer. It consists of three flat coils placed parallel to one another on a grad- uated rod, passing through their axes. The central coil, which is used as the primary of an induction coil, is fixed. The other two, which are employed as secondary coils, are movable. (See Sonometer, Hughes*. Coil, Induction. Micro- phone.} A microphone, electrical tuning fork, switches, plugs, and other accessories, are suitably placed and connected. The subject whose hear- ing is to be tested is placed with his back to tke apparatus, and with two telephone receivers tightly fixed to his ears. As various sounds are produced, the outer or movable coils are moved gradually away from the central coil, until no sound is heard in the telephone receivers. This distance is in the inverse ratio of the delicacy of hearing of the individual.

Actinic Photometer. — (See Photometer, Actinic?)

Actinic Ray.— (See Ray, Actinic?)

Actinism. — The chemical effects of light, as manifested by the decomposition of various substances.

Under the influence of the sun's light, the car- bonic acid absorbed by the leaves of plants is de- composed in the living leaves into carbon, which is retained by the plant for the formation of its woody fibre or ligneous tissue, and oxygen, which is thrown off.

Act,]

[Act.

The bleaching of curtains, carpets, and other fabrics exposed to sunlight is caused by the actinic power of the light. The photographic picture is impressed by the actinic power of light on a plate covered with some sensitive metallic salt.

Actinograph. — An apparatus for measur- ing and recording the intensity of the chemi- cal effects of light.

Actinography. — The method of measuring and recording the intensity of the chemical effects of light.

Actinometer. — A word sometimes applied to a pyrheliometer. (See Pyrheliometer)

Actinometer, Electric An appa- ratus for electrically measuring the intensity of the chemically active rays present in any luminous radiation.

The rays from the luminous source are per- mitted to fall on a selenium resistance, and their intensity determined by the change observed in the resistance as indicated by the deflections of a galvanometer placed in circuit with the selenium resistance. Or, a thermo-electric pile is employed, and the amount of heat present determined by the indications of a galvanometer placed in its circuit.

Action, Cataphoric The action

of electric osmose or cataphoresis. (See Cataphoresis.)

Action Currents. — (See Currents, Action?)

Action, Inductive, Lines of —

Lines within the space, separating a charge and a neighboring body, along which elec- trostatic inductive action takes place.

Lines of electrostatic force.

Lines of inductive action pass through the dielectric, separating the two bodies, and termi- nate on the surfaces of the conductor. According to the now generally received notions, the elec- trostatic charge exists in the mass of the dielectric, and not in that of the conductor. The lines of inductive action terminate against the surfaces, one at the positive, and the other at the negative surface. A true E. M. F. exists in the space traversed by lines of inductive action. A con- ductor brought into this space becomes electri- fied, or is strained in such a manner that a momentary current is produced by the rearrange-

ment of the electrification brought about by electrostatic induction.

Action, Local, of Dynamo-Electric Ma- chine The loss of energy in a dy- namo-electric machine by the setting up of eddy currents in its pole pieces, cores, or other conducting masses. (See Currents, Eddy.}

In a dynamo-electric machine local action is obviated by a. lamination of the pole pieces, arma- ture core, etc. (See Core, Lamination of.)

Action, Local, of Voltaic Cell

An irregular dissolving or consumption of the zinc or positive element of a voltaic battery, by the fluid or electrolyte, when the circuit is open or broken, as well as when closed, or in regular action.

Local action is due to small particles of such impurities as carbon, iron, arsenic, or other negative elements, in the positive plate. These impurities form with the positive element minute voltaic couples, and thus direct the corrosive action of the liquid to portions of the plate near them. Local action causes a waste of energy. It may be avoided by the amalgamation of the zinc. (See Zinc, Amalgamation of.)

Action, Magne-Crystallic A term

proposed by Faraday to express differences in the action of magnetism on crystalline bodies in different directions.

A needle of tourmaline, if hung with its axis horizontal, is no longer paramagnetic, as usual, but diamagnetic. The same is true of a crystal of bismuth. Faraday concluded from these ex- periments that a force existed distinct from either the paramagnetic or the diamagnetic force. He called this the magne crystallic force.

Pltlcker infers from these phenomena that a definite relation exists between the ultimate form of the particles of matter and their magnetic be- havior. The subject may be regarded as yet somewhat obscure. (See Polarity, Diamagnetic.}

Action of a Current on a Magnetic Pole.

— (See Current, Action of, on a Magnetic Pole) Action, Refreshing, of Current

The restoration, after fatigue, of muscular and nervous excitability obtained by the action of

Act.]

voltaic alternatives. (See Alternatives, Vol- taic)

Activity. — The work done per second by any agent. (This term is but seldom used.)

Work-per-second, or, as generally termed in the United States, Power, or Rate of Doing Work. (See Power.)

Activity, Unit of — —A rate of work- ing that will perform one unit of work per second.

In C. G. S. units, the activity of one erg per second.

The C. G. S. unit of activity is very small. One Watt, the practical unit of activity or power, is equal to ten million ergs per second. (See Watt.)

The unit of activity generally used for mechan- ical power is the horse-power, or 746 watts. (See Horse- Power.)

Actual Cautery.— (See Cautery, Actual)

Acute Angle. — (See Angle, Acute)

Adapter. — A screw nozzle fitted to an elec- tric lamp, provided with a screw thread to en- able it to be readily placed on a gas bracket or chandelier in place of an ordinary gas burner.

Adherence. — The quality or property of adhering. (See Adhesion)

Adherence, Magnetic Adhesion be- tween surfaces due to magnetic attraction.

Magnetic adhesion has been applied, among other things, to a brake action on car wheels, either by causing them to adhere directly to the track or to a brake-block.

Adhesion. — The mutual attraction which exists between unlike molecules. (See At- traction, Molecular?)

The phenomena of adhesion are due to the mutual attraction of dissimilar molecules.

Adhesion, Electric Adhesion be- tween surfaces due to the attraction of unlike electrostatic charges.

Molecular adhesion must be distinguished from the attraction which causes a piece of dry and warmed writing paper, that has been rubbed by a piece of india-rubber, to stick to a papered wall. In this latter case the attraction between the wall

[Aer.

and the paper is due to the mutual attraction of two dissimilar electrostatic charges. Molecular adhesion must also be distinguished from the at- traction of opposite magnetic poles.

Adhesion, Galvanoplastic -- The ad-

hesion of a galvanoplastic deposit or coating to surfaces subjected to electroplating. (See Plating, Electro)

Adiathermaiicy. — Opacity to heat.

A substance is said to be diathermanous when it is transparent to heat. Clear, colorless crys- tals of rock salt are very transparent both to light and to heat. Rock salt, covered with a layer or deposit of lampblack or soot, is quite transparent to heat. An adiathermanous body is one which is opaque to heat.

Heat transparency varies ndt only with differ- ent substances, but also with the nature of the source from which the heat is derived. Thus, a substance may be opaque to he it from a non- luminous source, such as a vessel filled with boil- ing water, while it is comparatively transparent to heat from a luminous source, such as an incan- descent solid or a voltaic arc.

A similar difference exists as regards transpar- ency to light. A colorless glass will allow light of any color to pass through it. A blue glass will allow blue light to pass freely through it, but will completely prevent the passage of any red light ; and so with other colors.

Adiathermauic. — Possessing the quality of adiathermancy. (See Adiathermancy)

Adjustable Condenser. — (See Condenser, Adjustable)

Adjuster, Cord --- A device for ad- justing the length of a pendant cord.

Adjustment. — Such a regulation of any apparatus as will enable it to properly perform its functions.

.Epinus' Condenser. — (See Condenser,

Aerial Cable.— (See Cable, Aerial) Aerial Cable, Suspending Wire of —

(See Wire, Suspending, of Aerial Cable) Aerial Line.— (See Line, Aerial.) Aerolites. — A name sometimes given to

meteorites. Meteorites are masses of solids which pass

Aff.]

10

[Ago.

through the upper portions only of the earth's atmosphere on their approach to the orbit of the earth, or which fall through the air on the earth's surface from the sky. They are luminous at night and are followed by a train of fire. The luminosity is due to heat produced by friction through the air. Meteors frequently burst from the sudden expansion of their outer portions.

Some meteorites are composed of nearly pure iron alloyed with nickel. The majority of them, however, are merely stones or oxidized sub- stances. Their average velocity is about 26 miles a second.

Affinity, Chemical — —Atomic attrac- tion.

The force which causes atoms to unite and form chemical molecules.

Atomic or chemical attraction generally results in a loss of the characteristic qualities or proper- ties which distinguish one kind of matter from another. In this respect chemical affinity differs from adhesion, or the force which holds unlike molecules together. (See Adhesion. Attraction, Molecular.} If, for example, sulphur is mixed with lampblack, no matter how intimate the mixture, the separate particles, when examined by a magnifying glass, exhibit their peculiar color, lustre, etc. If, however, the sulphur is chemi- cally united with the carbon, a colorless, transpar- ent, mobile liquid, called carbon bisulphide, re- sults, that possesses a disagreeable, penetrating odor.

Chemical affinity, or atomic combination, is in fluenced by a variety of causes, viz. :

(I.) Cohesion. Cohesion, by binding the mole- cules more firmly together, opposes their mutual atomic attraction.

A solid rod of iron will not readily burn in the flame of an ordinary lamp ; but, if the cohesion be overcome by reducing the iron rod to filings, it burns with brilliant scintillations when dropped into the same flame. In this case the increase of surface and the increased temperature of the smaller particles also contribute to the result.

(2.) Solution. Solution, by giving the molecules greater freedom of motion, favors their chemical combination.

(3.) Heat. Heat sometimes favors atomic com- bination possibly by decreasing the cohesion, and, possibly, by altering the electrical relations of the atoms. If too great, heat may produce decom- position. There is for most substances a critical

temperature below wh^h chemical combination will not take place. (See Thermolysis. )

(4.) Light. Decomposition, or the lessening of chemical affinity, through the agency of light, is called Actinism, Light also causes the direct combination of substances. A mixture of equal volumes of hydrogen and chlorine unites explo- sively when exposed to the action of full sunlight. (See Actinism.)

(5.) Electricity. An electric spark will cause an explosive combination of a mixture of oxygen and hydrogen. Electricity also produces chemi- cal decomposition. (See Electrolysis.)

Helmholtz accounts for the electro-chemical attraction of oxygen for zinc by supposing that all substances possess a definite amount of attraction for electricity, and that the attraction of zinc in this respect exceeds that of copper and the other metals. He thus regards the zinc as attracting its electric charge rather than as attracting the oxygen. Since both zinc and copper are dyad metals, this view, as will be seen, is at variance with later views.

Chemical affinity may be caused by the opposite attractions of electrical charges naturally possessed by the atoms of matter. This would appear to be rendered probable by the law of electro-chemical equivalence. (See Equivalence, Electro-Chemical, Law of. Electricity, Atom of.)

After Currents.— (See Currents, After.}

Aging of Alcohol, Electric (See

Alcohol, Electric Aging of.)

Agonal.— Pertaining to the agone. (See Agone.)

Agone. — A line connecting places on the earth's surface where the magnetic needle points to the true geographical north.

The line of no declination or variation of a magnetic needle. (See Needle, Magnetic, Declination of.)

As all the places on the earth where the mag- netic needle points to the true north may be ar- ranged on a few lines, it will be understood that the pointing of the magnetic needle to the true geographical north is the exception and not the rule. In many places, however, the deviation from the true geograpical north is so small that the direction of the needle may be regarded as approximately due north.

Agonic. — Pertaining to the agone.

Air.

11

[Ala.

Air-Blast for Commutators. — An inven- tion of Prof. Elihu Thomson to prevent the injurious action of destructive flashing at the commutator of a dynamo-electric machine.

A thin, forcible blast of air is delivered through suitable tubes at points on the three-part commu- tator cylinder of the Thomson- Houston dynamo, where the collecting brushes bear on its surface. The effect is to blow out the arc or prevent its for- mation and thus avoid its destructive action on the commutator segments. The use of the air- blast also permits the free application of oil, thus further avoiding wear.

Fig. 4. Air-Blast on Commuta The blast-nozzles are shown at B3, B8, Fig. 4, near the collecting brushes.

The air-supply is obtained from a blower at- tached directly to the shaft of the machine. Its construction and operation will be readily under- stood from an inspection of Fig. 5, in which the

Fig. f. The Thomson Blower.

top is removed for ready examination of the interior parts.

Air Churning. — (See Churning, Air)

Air Condenser. — (See Condenser, Air)

Air Field.— (See Field, Air)

Air-Gap.— (See Gap, Air)

Air-Line Wire.— (See Wire, Air-Line)

Air Magnetic Circuit.— (See Circuit, Air Magnetic)

Air-Pump.— (See Pump, Air)

Air-Pump, Oeissler's Mercurial

(See Pump, Air, Geissler's Mercurial)

Air-Pump, Mechanical (See Pump,

Air, Mechanical)

Air-Pump, Mercurial (See Pump,

Air, Mercurial)

Air-Pump, Sprengel's Mercurial

(See Pump, Air, SprengeFs Mercurial)

Air-Space Cut-Out— (See Cut-Out, Air- Space)

Alarm, Burglar A device, generally

electric, for automatically announcing the opening of a door, window, closet, drawer, or safe, or the passage of a person through a hallway, or on a stairway.

Electric burglar-alarm devices generally consist of mechanism for the operation of an automatic make -and -break bell on the opening or closing of an electric circuit. The bell may either continue ringing only while the contact remains closed, or, may, by the throwing on of a local circuit or battery, continue ringing until stopped by some non-automatic device, such as a hand-switch.

The alarm-bell is stationed either in the house when occupied, or on the outside when the house is temporarily vacated, or may connect directly with the nearest police station.

Burglar-alarm apparatus is of a variety of forms. Generally, devices are provided by means of which, in case of house protection, an annunci- titor shows the exact part where an entrance has been attempted. (See Annunciator, Burglar- Alarm) Switches are provided for disconnecting all or parts of the house from the alarm when so desired, as well as to per- mit windows to be partly raised for purposes of ven- tilation without sounding the alarm. A clock is fre- quently connected with the alarm for the purpose of automatically disconnect- ing any portion of the house at or for certain in- tervals of time.

Fig. 6 shows a burglar- Fig. 6. Burglar-Alarm alarm with annunciator, Annunciator.

switches, switch-key, cut-off, and clock.

Alarm, Burglar, Central-Station

A burglar-alarm, the contact points of which are placed in the places to be protected, and

Ala.]

[Ate.

connected by suitable circuits with alarms placed in a centrally located station.

In a system of central-station burglar-alarms, a number of houses, factories, banks, etc., are all connected telegraphically with the nearest police station, or other central station, constantly pro- vided with police officers. A series of contacts are placed on doors, windows, safes and money draw- ers, and connected with alarms and annunciators placed in the central station. An unauthorized entrance, therefore, is automatically telegraphed to the central station and its exact location indi- cated on the annunciator. Systems of central- station fire-alarms are constructed on a similar plan.

Alarm, Electric An automatic de- vice by which attention is called to the occur- rence of certain events, such as the opening of a door or window; the stepping of a person on a mat or staircase; the rise or fall of tem- perature beyond a given predetermined point; or, a device intended to call a person to a tel- egraphic or telephonic instrument.

Electric-alarms are operated by means of the ringing of an electro-magnetic or mechanical bell,

Fig. 7. Electrically Started Mechanical Alarm.

which is electrically called into action by either closing or opening an electric circuit, generally the former.

Electric-alarms may be divided into two classes, viz.:

(I.) Mechanically operated alarms, or those in

which the alarm is given by clock-work, started by means of an electric current.

(2.) Those in which the alarm is both set in ac- tion and operated by an electric current.

In Fig. 7 is shown the general construction of an electrically started mechanical alarm. The attraction of the armature B, by the electro-mag- net A, moves the armature lever pivoted at C, and thus releases the catch e, and permits the spring or weight connected with the clock move- ment to set it in motion and strike the bell.

Electrically actuated alarm-bells are generally of the automatic make-and-break form. The striking lever is operated by the attraction of the armature of an electro-magnet, and is provided with a contact-point, so placed that when the hammer is drawn away from the bell, by the ac- tion of a spring, on the electro-magnet losing its magnetism, a contact is made, but when the ham- mer is drawn towards the bell the contact is open- ed. When, therefore, the hammer strikes the bell, the circuit is opened, and the electro-magnet releases its armature, permitting a spring to again close the contact by moving the striking lever away from the bell. Once set into action, these movements are repeated while there is battery power sufficient to energize the magnet.

In Fig. 8, in which is shown an electrically ac- tuated alarm-bell, the battery terminals are con-

Fig. 8. Automatic Make-and-Break.

..ected with the right and left hand binding-posts, P and M. The hammer, K, is connected with a striking lever, which forms part of the circuit," and which is attached toihe armature of the elec tro-magnet e. A metallic spring, g, bears against the armature when the latter is away from the magnet, but does not touch the armature when it is moved towards the magnet. A small spring draws the lever away from the magnet when no current is passing. The movements of the arma

13

[AlCo

ture thus automatically open and close the circuit of the electro-magnet.

This form of make-and-break is called an auto- matic make-and-break.

Alarm, Electrically Operated — —An

alarm that is maintained in operation by the electric current. (See Alarm, Electric^)

Alarm, Electro-Mechanical - - —A mechanically operated alarm that is started or set in operation by means of an electric current. (See Alarm, Electric^)

Alarm, Fire, Automatic An in- strument for automatically telegraphing an alarm from any locality on its increase in tem- perature beyond a certain predetermined point.

Fire-alarms are operated by thermostats, or by means of mercurial contacts; i. e., a contact closed by the expansion of a column of mercury. (See Thermostat. Contact, Mercurial.)

In systems of fire-alarm telegraphs, the alarm is automatically sounded in a central police sta- tion and in the district fire-engine house. (See Telegraphy, Fire-Alarm. )

Alarm, Mercurial Temperature

An instrument for automatically telegraphing an alarm by means of a mercurial contact on a predetermined change of temperature.

The action of mercurial contacts is dependent on the fact that, as the mercury expands more than glass by the action of heat, the mercury level reaches a contact-point placed in a glass tube and thus completes the circuit through its own mass, which forms the other or movable contact. Sometimes both contacts are placed on opposite sides of a tube and are closed when the mercury reaches them.

Mercurial temperature or thermostat alarms are employed in hot-houses, incubators, tanks and buildings for the purpose of maintaining a uniform temperature.

Alarm, Telegraphic — — An alarm-bell for calling the attention of an operator to a telegraphic instrument when the latter is of the non-acoustic or needle type.

In acoustic systems of telegraphy the sounds themselves are generally sufficient.

Alarm, Telephonic An alarm-bell

for calling a correspondent to the receiving telephone.

These alarms generally consist of magneto- electric bells. (See Bell, Magneto-Electric.)

Alarm, Temperature — —An electric alarm automatically operated on a change of temperature. (See Alarm, Fire, Automatic)

Alarm, Thermostat— —An electric alarm that is thrown into action by a thermo- stat. (See Thermostat)

Alarm, Water or Liquid Level

A device for electrically sounding an alarm wnen a water surface varies materially from a given level.

An electric bell is placed in a circuit that is au- tomatically closed or broken by the movement of contact-points operated by the change of liquid level.

A form of electric alarm for a water-level is shown in Fig. 9. The float is provided with contacts for closing an electric circuit, when it either rings a bell, or, by its action on some form of automatic cut-off, stops the water.

Fig: 9. Water- Level Alarm. Fig. 10.

When arranged with a double float, as shown in Fig. 10, the alarm may be made to signal either a too high or a too low water level.

Alarm, Yale-Lock-Switch Burglar — — An apparatus whereby the opening of a door by an authorized party provided with the regular key will not sound an alarm, but any other opening will sound such alarm.

Fig. n. Yale-Lock-Switch.

A Yale-lock burglar-alarm switch is shown in Fig. II.

Alcohol, Electric Aging of A pro- cess for the rapid aging of alcohol, by rx-

Ale.]

14

[All.

posing it to the action of electrically produced ozone.

Instead of the ordinary process of aging alco- hol, by exposing it in partially closed vessels to the action of air, it is exposed to the action of ozone, electrically produced.

The ozone employed is obtained in substan- tially the usual way by the passage of a rapid succession of electric sparks through air.

Alcohol, Electric Rectification of —

A process whereby the bad taste and odor of alcohol, due to the presence of aldehydes, are removed by the electrical conversion of the aldehydes into true alcohols through the addition of hydrogen atoms.

An electric current sent through the liquid between zinc electrodes liberates oxygen and hy- drogen from the decomposition of the water. The nascent or atomic hydrogen converts the aldehydes into alcohol and deprives the pro- ducts of their fusel oil, while the oxygen forms insoluble zinc oxide.

Algebraic Co-efficient— (See Co-efficient, Algebraic?)

Algebraic Notation.— (See Notation, Al- gebraic?)

All-Night Arc Lamp.— (See Lamp, All- Night Arc?)

All-Night Electric Lamp.— (See Lamp, All-Night Arc.}

Allotropic.— Pertaining to allotropy. (See Allotropy.}

Allotropic State.— (See State, Allotropic).

Allotropy. — A variation of the physical properties of an elementary substance with- out change of composition of its molecules.— (See State, Allotropic.)

Alloy. — A combination, or mixture, of two or more metallic substances.

Alloys in most cases appear to be true chemi- cal compounds. In a few instances, however, they may form simple mixtures.

The composition of a few important alloys is here given:

Solder, plumber's; Tin 66 parts, Lead 34 parts.

Pewter, hard; Tin 92 parts, Lead 8 parts.

Britannia metal; Tin 100 parts, Antimony 8 parts, Copper 4 parts, Bismuth, I part.

Type metal; Lead 80, Antimony 20 parts. Brass, white; Copper 65, Zinc 35 parts. Brass, red; Copper 90, Zinc I o parts. Speculum metal ; Copper 67, Tin 33 parts. Bell metal; Copper 78, Tin 22 parts. Aluminium bronze; Copper 90, Aluminium 10 parts.

Alloy. — To form a combination or mixture of two or more metallic substances.

Alloy, German Silrer — An alloy

employed for the wires of resistance coils, consisting of 50 parts of copper, 25 of zinc, and 25 of nickel.

German silver wire is suitable for resistance coils, because its resistance varies but slightly with changes of temperature. It is cheaper than plati- num-silver alloy, and is therefore employed ex- tensively. Platinum silver alloy, however, has more resistance for a given size of wire, and its re- sistance varies somewhat less than German silver with changes of temperature, and is therefore used where greater accuracy is desired.

Alloy, Palladium An alloy of pal- ladium with other metals.

Palladium forms a number of useful alloys with various metals. Some of the palladium alloys are as elastic as steel, are unaffected by moisture or ordinary corrosive agencies, and are entirely de- void of paramagnetic properties; that is to say, they cannot be magnetized after the manner of iron.

These properties have been utilized by their discoverer, Paillard, in their employment for the hair-springs, escapements and balance wheels of watches, in order to permit the watches to be car- ried into strong magnetic fields without any ap- preciable effects on the rate of the watch. A number of careful tests made by the author, by long continued exposure of watches, thus pro- tected by the Paillard alloys, in extraordinary fields, show that the protection thus given the watches enables them to be carried into the strong- est possible magnetic fields without appreciably affecting their rate.

The Paillard palladium alloys have the follow- ing composition, viz.:

Alloy No. i.

Palladium 60 to 75 parts.

Copper 151025 "

Iron i to 5 "

All.]

15

[Alp.

Alloy No. 2. Palladium .............. 50 to 75 parts.

Copper 20 to 30 "

jron c to 20 "

Alloy No. j. Palladium .............. 65 to 75 "

,

Copper ................ 151025 "

Nickel ................ ito 5 "

Gold .................. ito 2* «

Platinum ............... i to 2 "

Silver .................. 3toio «

Steel .............. i to 5 "

Alloy No. 4.

Palladium .............. 45 to 50 "

Silver .................. 201025 "

Copper ................ l5to2S <«

Gold ................... 2 to 5 "

Platinum ............... 2 to 5 "

Nickel ................. 2105 "

Steel ................... 2 to 5 "

The great value of the palladium alloys, when employed for the hair-springs of watches, arises not only from their non -magnetizable properties, and their inoxidizability, but particularly from the fact that their elasticity is approximately the same for comparably wide ranges of temperature.

Alloy, Platinum-Silver -- An alloy consisting of one part of platinum, and two parts of silver.

Platinum- silver alloy is now extensively em- ployed for resistance coils from the fact that changes in temperature of the alloy produce but comparatively small changes in its electrical re- sistance. (See Alloy, German Silver.}

Alphabet, Telegraphic -- An arbi- trary code consisting of dots and dashes, sounds.deflections of a magnetic needle, flashes of light^ or movements of levers, following one another in a given predetermined order, to represent the letters of the alphabet and the numerals.

Alphabet, Telegraphic: International

n A T-i. j t • if i

Code -- The code of signals for letters,

etc., employed in England and on the Euro- pean continent generally.

Similar symbols are employed for the numerals and the punctuation marks.

It will be observed that it is mainly in the

characters of the American Morse, in which spaces ** used> that the Continental characters differ from the American. This is due to the use of the needle instrument, with which a space cannot well be represented. A movement or deflection of the

S'nK'e *"**

Printing Needle Printing .Needle

* — x/ n— <\

* — •'- o --- "/ c~* — /X/N p --- • *'' x «— '- « ---- ^

International Telegraphic Code.

needle to the left signifies a dot; a movement to the right» a dash-

Alphabet, Telegraphic : Morse's __

Varkms ^ of dots and dashes> Qr

deflections of a ma tic needle to the rf ht ^ ^ ^.^ represent ^ lettere Q£ ^

alphabet or other signs.

In t^ Morse alphabet dots and dashes are em- ployed in recording systems, and sounds of varying intervals, corresponding to the dots and dashes, in the sounder system.

A dash is equal in length of time to three dots. The space between the separate characters of a single letter is equal to one dot, except in the American Morse, in which the following letters contain longer spaces: c> o> R? Y> and z. The

lengthened spaces are equal to two dots. L is one and a half times the length of T.

The sound produced by the down stroke of the sounding lever in the Morse sounder is readily distinguishable from the up stroke. When these differences are taken in connection with the inter- vals between successive sounds there is no diffi-

culty in reading by sound. (For methods of recdving the alphabet> see

Sounder, Morse Telegraphic. Recorder, Morse. Recorder, BaMs Chemical. Recorder, Siphon. Relay. Magnet, Receiving. ) In the needle tele- graph, the code is similar to that used in the Morse Alphabet. (See Telegraphy, Single-Needle.}

Alt.]

AMERICAN MORSE CODE. ALPHABET.

h ---.

o - -

P

q

r - --

s

t —

u

v

w

m

& - ---

NUMERALS. i

2

3

4

PUNCTUATION MARKS.

Period

Comma

Interrogation

Exclamation

Printing

SingJe Needle X ////

xx /// xxx // xxxx/

10

Period ------ NX \\ \x

Comma ______ x A A /

Interrogation ______ xx / / \\

Exclamation ______ /Ax//

Colon ______ ///NNN

Semicolon ______ /\/\/\

Alteration Theory of Muscle or Nerve Current— (See Theory, Alteration, of Muscle or Nerve Current?)

Alternating Arc. — (See Arc, Alternat- ing.}

Alternating Current Circuit.— (See Cir- cuit, Alternating Current?)

16 [Alt.

Alternating Current Condenser. — (See Condenser, Alternating Current?)

Alternating Current Dynamo-Electric Machine. — (See Machine, Dynamo-Electric, Alternating Current?)

Alternating Current Electric Motor.—

(See Motor, Electric, Alternating Current?)

Alternating Currents. — (See Currents, Alternating?)

Alternating Currents, Distribution of Electricity by — —(See Electricity, Dis- tribution of, by Alternating Currents?)

Alternating Discharge. — (See Discharge, Alternating?)

Alternating Dynamo-Electric Machine. — (See Machine, Dynamo-Electric, Alternat- ing Current?)

Alternating Electrostatic Field.— (See Field, Alternating Electrostatic?) ,

Alternating Electrostatic Potential.— (See Potential, Alternating Electrostatic?)

Alternating Field.— (See Field, Alternat- ing?)

Alternating Influence Machine, Wims- hurst's — — (See Machine, Wimshurst's Alternating Influence?)

Alternating Magnetic Field.— (See Field, Alternating Magnetic?)

Alternating Magnetic Potential.— (See Potential, Alternating Magnetic?)

Alternating Potential.— (See Potential, Alternating?)

Alternating Primary Currents. — (See Currents, Alternating Primary?)

Alternating Secondary Currents.— (See Currents, Alternating Secondary?)

Alternation. — A change in direction or phase.

Alternations. — Changes in the direction of a current in a circuit.

A current that changes its direction 300 times per second is said to possess 300 alternations per second.

Alternations, Complete — —A change in the direction of a current in a circuit from its

Alt]

[A mm.

former direction and back again to that direction. A complete to-and-fro change.

Complete alternations are sometimes indicated by the symbol ~.

Alternations, Frequency of — A

phrase employed to denote the number of al- ternations per second.

Alternative Path.— (See Path, Alterna- tive^

Alternatives, Yoltaic A term used

in medical electricity to indicate sudden re- versals in the polarity of the electrodes of a voltaic battery.

An alternating current from a voltaic bat- tery, obtained by the use of a suitable com- mutator.

Sudden reversals of polarity produce more energetic effects of muscular contraction than do simple closures or completions of the circuit.

The muscular contraction produced by a voltaic current is much stronger when the direction of the current is rapidly reversed by means of a com- mutator than when the current is more slowly broken and the poles then reversed.

The effect of voltaic alternatives is to produce quick contractions that are in strong contrast to the prolonged contractions that result from the faradic current. In the faradic machine, the reversals are so rapid that the muscle fails to return to rest before it is again contracted.

Voltaic alternatives are sometimes indicated by the contraction V. A.

Alternator. — A name commonly given to an alternate current dynamo. (See Machine, Dynamo-Electric, Alternating Current?)

Alternator, Compensated Excitation of

— An excitation of an alternating current dynamo-electric machine, in which the field is but partially excited by separate excitement, the remainder of its exciting current being derived from the commuted currents of a small transformer placed in the main circuit of the machine.

The object of compensated excitation of an alternator is to render the machine self-governing.

Amalgam. — A combination or mixture of a metal with mercury.

Amalgam, Electric — A substance

with which the rubbers of the ordinary fric- tional electric machines are covered.

Electric amalgams are of various compositions. The following formula produces an excellent amalgam :

Melt together five parts of zinc and three of tin, and gradually pour the molten metal into nine parts of mercury. Shake the mixture until cold, and reduce to a powder in a warm mortar. Apply to the cushion by means of a thin layer of stiff grease.

Mosaic gold, or bisulphide of tin, and powdered graphite, both act as good electric amalgams.

An electric amalgam not only acts as a con- ductor to carry off the negative electricity, but, being highly negative to the glass, produces a far higher electrification than would mere leather or chamois.

Amalgamate. — To form into an amalgam.

Amalgamating. — Forming into an amal- gam.

Amalgamation. — The act of forming into an amalgam, or effecting the combination of a metal with mercury.

Amalgamation of Zinc Plates of Yoltaic Cell.— (See Plates, Zinc, of Voltaic Cell, Amalgamation of,}

Amber. — A resinous substance, generally of a transparent, yellow color.

Amber is interesting electrically as being be- lieved to be the substance in which the proper- ties of electric attractions and repulsions, imparted by friction or rubbing, were first noticed. It was called by the Greeks r/\Enrpov, from which the word electricity is derived. This property was mentioned by the Greek, Thales of Miletus, 600 B. c., as well as by Theophrastus.

American System of Telegraphy.— (See Telegraphy, American System of.)

American Twist-Joint— (See Joint, American Twist?)

American Wire Gauge. — (See Gauge, Wire, American?)

Ammeter. — A form of galvanometer in which the value of the current is measured directly in amperes. (See Galvanometer?)

An ampere-meter or ammeter is a commercial form of galvanometer in which the deflections* of

Amm.J

18

[Amp.

a magnetic needle are calibrated or valued in am- peres. As a rule the coils of wire in an ammeter are of lower resistance than in a voltmeter. The magnetic needle is deflected from its zero position by the field produced by the current whose strength in amperes is to be measured. This needle is held in the zero position by the action of a magnetic field, either of a permanent or an electro-magnet, by the action of a spring, or by a weight under the influence of gravity. There thus exist a variety of ammeters, viz. : permanent-magnet ammeters, electro-magnetic ammeters, spring ammeters and gravity ammeters.

In the form originally devised by Ayrton and Perry, the needle came to rest almost imme- diately, or was dead-beat in action. (See Damp- ing.') It moved through the field of a permanent magnet. The instrument was furnished with a number of coils of insulated wire, which could be connected either in series or in multiple-arc by means of a commutator, thus permitting the scale reading to be verified or calibrated by the use of a single voltaic cell. (See Circuits, Varieties of. Commutator. Calibration, Absolute. Calibra- tion, Relative.) In this case the coils were turned to series, and a plug pulled out, thus intro- ducing a resistance of one ohm.

c

Fig. ra. Ayrton and Perry Ammeter.

Fig. 12 represents an ampere-meter devised by Ayrton and Perry. A device called a commutator for connecting the coils either in series or parallel is shown at C. Binding-posts are provided at P, PS, and S. The dynamo terminals are con- nected at the posts P, PS, and the current will pass only when the coils are in multiple, thus avoiding accidental burning of the coils. In this case the entire current to be measured passes through the coils so coupled. The posts S and PS, are for connecting the single battery cell cur- rent.

A great variety of ampere-meters, or ammeters, have been devised. They are nearly all, how-

ever, constructed on essentially the same general principles.

Commercial ammeters are made in a great va- riety of forms. When the currents to be meas- ured are large, as is generally the case in electric light or power stations, they consist of a coil of insulated wire, often of a single turn, or even of but a part of a turn, having a balanced core of iron or steel capable of moving freely within it.

Ammeter, Electro-Magnetic A

form of ammeter in which a magnetic needle is moved against the field of an electro-magnet by the field of the current it is measuring. (See Ammeter?)

Ammeter, Gravity A form of am- meter in which a magnetic needle is moved against the force of gravity by the field of the current it is measuring. (See Ammeter?)

Ammeter, Magnetic- Vane An

ammeter in which the strength of a magnetic field produced by the current that is to be measured is determined by the repulsion ex- erted between a fixed and a movable iron vane, placed in said field and magnetized thereby. (See Voltmeter, Magnetic- Vane.}

Ammeter, Permanent-Magnet A

form of ammeter in which a magnetic needle is moved against the field of a permanent mag- net by the field of the current it is measuring. (See Ammeter?)

Ammeter, Reducteur for (See Re-

ducteur, or Shunt for Ammeter?)

Ammeter, Spring A form of am- meter in which a magnetic needle is moved against the action of a spring by the field of the current it is measuring. (See Ammeter.}

Amorphous. — Having no definite crys- talline form.

Mineral substances have certain crystalline forms, that are as characteristic of them as are the forms of animals or plants. Under certain cir- cumstances, however, they occur without definite crystalline form, and are then said to be amor- phous solids.

Amperage. — The number of amp&res pass- ing in a given circuit.

The current strength in any circuit as indi- cated by an ampere-meter placed in the circuit.

Amp.]

19

[Amp.

Ampere. — The practical unit of electric current.

Such a rate-of-flow of electricity as trans- mits one coulomb per second.

Such a current (or rate-of-flow or trans- mission of electricity) as would pass with an electromotive force of one volt through a cir- cuit whose resistance is equal to one ohm.

A current of such a strength as would deposit .005084 grain of copper per second.

A current of one ampere is a current of such definite strength that it would flow through a cir- cuit of a certain resistance and with a certain electromotive force. (See Force, Electromotive. Volt. Resistance. Ohm.}

Since the ohm is the practical unit of resistance, and the volt the practical unit of electromotive force, the ampere, or the practical unit of current, is the current that would flow through unit resist- ance, under unit pressure or electromotive force.

To make this clearer, take the analogy of water flowing through a pipe under the pressure of a column of water. That which causes the flow is the pressure or head ; that which resists the flow is the friction of the water against the pipe, which will vary with a number of circumstances. The rate-of-flow may be represented by so many cubic inches of water per second.

As the pressure or head increases, the flow in- creases proportionally; as the resistance increases, the flow diminishes.

Electrically, electromotive force corresponds to the pressure or head of the water, and resistance to the friction of the water and the pipe. The ampere, which is the unit rate-of-flow per second, may therefore be represented as follows,

viz. : C = _, as was announced by Ohm in his R

law. (See Law of Ohm.}

This expression signifies that C, the current in amperes, is equal to E, the electromotive force in volts, divided by R, the resistance in ohms.

We measure the rate-of-flow of liquids as so many cubic inches or cubic feet per second — that is, in units of quantity. We measure the rate-of-flow of electricity as so much electricity per second. The electrical unit of quantity is called the Coul- omb. (See Coulomb.} The coulomb is such a quantity as would pass in one second through a circuit in which the rate-of-flow is one ampere.

An ampere is therefore equal to one coulomb per

The electro-magnetic unit of current is such a current that, passed through a conducting wire bent into a circle of the radius of one centimetre, would tend to move perpendicular to its plane a unit magnetic pole held at its centre, and sufficiently long to practically remove the other pole from its influence, with unit force, i. <?., the force of one dyne. (See Dyne.) The ampere, or practical electro-magnetic unit, is one-tenth of such a current ; or, in other words, the absohite unit of current is ten amperes.

An ampere may also be defined by the chemical decomposition the current can effect as measured by the quantity of hydrogen liberated, or metal deposited.

Defined in this way, an ampere is such a cur- rent as will deposit .00111815 gramme, or .017253 grain, of silver per second on one of the plates of a silver voltameter, from a solution of silver nitrate containing from 15 to 30 per cent, of the salt (See Voltameter], or which will decompose .00009326 gramme, or .001439 grain of dilute sulphuric acid per second, or pure sulphuric acid at 59 degrees F. diluted with about 15 per cent, of water, that is, dilute sulphuric acid of Sp. Gr. of about I.I. The present scientific and commercial practice is to take the ampere to be such a current as will deposit 4. 024 grammes of silver in one hour.

Ampere Arc. — (See Arc, Ampere?) Ampdre-Feet.— (See Feet, Ampere.} AmpSre-Hour. — (See Hour, Ampere.}

Ampere-Meter. — An ammeter. (See Am- meter.}

Ampere-Meter, Balance or Neutral Wire

An ampere-meter placed in the cir- cuit of the neutral wire, in the three-wire sys- tem of electric distribution, for the purpose of showing the excess of current passing over one side of the system as compared with the_ other side, when the central wire is no longer neutral.

Ampere-Minute. — (See Minute, Ampere} Ampere Ring. — (See king, Ampere?) Ampere-Second. — (See Second, Ampere?) Ampdre Tap7— (See Tap, Ampere?) Ampere-Turn. — (See Turn, Ampere?)

Ampere-Turn, Primary (See Turn,

Ampere, Primary?)

Amp.]

20

[Ane.

Ampere-Turn, Secondary — (See

Turn, Ampere, Secondary?)

Ainpdre-Yolt. — A watt, or the -7-5^ of a horse-power.

This term is generally written volt-ampere. (See Volt-Ampere.}

Ampdre-Winding. — (See Winding, Am- pere)

Ampere's Bule for Effect of Current on Needle.— (See Rule, Amperes, for Effect of Current on Needle?)

Ampere's Theory of Magnetism. — (See Magnetism, Ampere's Theory of)

Amperian Currents. — (See Currents, Am- perian)

Amplitude of Vibration or Wave.— (See Vibration or Wave, Amplitude of)

Ammunition-Hoist, Electric An

electrically operated hoist for raising ammu- nition to the deck of a ship.

In the electric ammunition-hoist the electric motor which moves the hoist is made to follow the motions of the operator's hand, both as regards direction and speed. The motion of a crank, or wheel, causes a switch to start an electric motor in a certain direction, which tends to close the switch, thus necessitating a race between the operator and the motor. Shpuld the operator begin to close the switch more slowly, the motor will over- take him, will partially close the switch, and thus * lower the speed of the motor.

Analogous Pole. — (See Pole, Analogous)

Analysis. — The determination of the com- position of a compound substance by separ- ating it into the simple or elementary sub- stances of which it is composed.

Analysis, Electric The determin- ation of the composition of a substance by electrical means.

Various processes have been proposed for elec- tric analysis; they consist essentially in decompos- ing the substance by means of electric currents, and are either qualitative or quantitative. (See Electrolysis . )

Analysis, Electrolytic A term

sometimes used instead of electric analysis. (See Analysis, Electric)

Analysis, Qualitative A chemical

analysis which merely ascertains the kinds of elementary substances present.

Analysis, Quantitative A chemical

analysis which ascertains the relative propor- tions in which the different components enter into a compound.

Analyzable. — Separable into component parts.

Analyze. — To separate into component parts.

Analyze, Electrically To separate

electrically into component parts.

Analyzer, Electric A gridiron of

metallic wires which is transparent to electro- magnetic waves, when its length is perpendic- ular to them, but opaque to them — /. e., possessing the ability to reflect them — when rotated 90 degrees from its former position.

The electric analyzer, it will be observed, is analogous to an analyzer for polarized light. A reflecting surface, for example, being able to re- flect polarized light in a given position, and unable to reflect it when rotated 90 degrees from such position, is capable of acting as an analyzer for pjlarized light.

Analyzer, Gray's, Harmonic Telegraphic

An electro-magnet, the armature of

which consists of a steel ribbon stretched in a metallic frame and capable through regula- tion, as to tension, by means of a screw, of being tuned to a certain note.

The steel ribbon is thrown into vibration when- ever pulsations from the transmitting instruments are sent over the line corresponding to the rate of motion of the ribbon, but is not set into vibration by any others. If, therefore, a number of different analyzers, tuned to different notes, are placed on the same line, each will be operated only by the pulsations sent into the line corresponding to its rate of motion, and thus multiple transmission in the same direction is possible. In order to strengthen the tones of the analyzers, each is pro- vided with a resonant air column. (See deton- ator. Telegraphy, Multiplex)

Analyzing. — Separating into component parts.

Anelectric. — A word formerly applied to bodies (conductors) which it was believed could not be electrified by friction.

Ane.]

[Ani.

This term is now obsolete. Conductors are easily electrified, when insulated.

Anelectrotonic State.— (See State, Anelec- trotonic)

Anelectrotonic Zone. — (See Zone, Anelec- trotonic^)

Anelectrotonus. — In electro-therapeutics, the decreased functional activity which occurs in a nerve in the neighborhood of the anode, or positive electrode, when applied therapeu- tically. (See Electrotonus)

Anemometer, Electric An appa- ratus to electrically record or indicate the direc- tion and intensity of the wind.

In the electric recording anemometer, the force or velocity of the wind, or both, are recorded on a moving sheet of paper, on which the time is marked, so that the exact time of any given change is known.

Anemoscope. — An instrument which indi- cates, but does not measure the intensity or record the direction of the wind.

The word is often, though improperly, used in- terchangeably for anemometer.

Angle. — The deviation in direction between two lines or planes that meet.

Angles are measured by arcs of circles. The angle at B A C, Fig. 13, is the deviation of the

straight line A B, from A C. In reading the let- tering of an angle the letter placed in the mid- dle indicates the angle referred to. Thus B A

C, means the angle be- D~

tween A B and A C ; B A Fig- 13- Angles.

D, the angle between B A and A D. Angles are valued in degrees, there being 360 degrees in an entire circumference or circle. Degrees are in- dicated thus: 90°, or ninety degrees.

Angle, Acute An angle whose value

is less than a right angle or 90 degrees.

B A E, or E A D, in Fig. 13, is an acute angle.

Angle, Complement of — —What an angle needs to make its value 90 degrees, or a right angle.

Thus in Fig. 13, B A E, is the complement of the angle E A D, since BAE4-EAD = 9O degrees.

Angle, Obtuse An angle whose

value is greater than a right angle or 90 degrees.

E A C, Fig. 13, is an obtuse angle.

Angle of Declination or Variation. — (See Declination, Angle of. Variation, Angle of.)

Angle of Difference of Phase Between Alternating Currents of Same Period. — (See Phase, Angle of Difference of, Between Alternating Currents of Same Period?)

Angle of Dip.— (See Dip. Dip or Incli- nation, Angle of)

Angle of Inclination.— (See Dip or Incli- nation, Angle of)

Angle of Lag of Dynamo-Electric Ma- chine.— (See Lag, Angle of, of Dynamo- Electric Machine)

Angle of Lead.— (See Lead, Angle of)

Angle of Variation.— (See Variation, Angle of.}

Angle, Plane An angle contained

between two straight lines.

Angle, Solid An angle contained

between two surfaces.

Angle, Supplement of What an

angle needs to make its value 180 degrees, or two right angles.

Thus in Fig. 13, E A C, is the supplement of E A D, because EAD-f-EAC = i8o degrees, or two right angles.

Angle, Unit An angle of 57.29578°

or 57° 17' 44.8" nearly. — (See Velocity, An- gular.)

Angnlar Currents. — (See Currents, An- gular.)

Angular Velocity.— (See Velocity, Angu- lar)

Animal Electricity.— (See Electricity, Animal)

Animal Magnetism.— (See Magnetism, Animal)

Anion. — The electro-negative radical of a molecule.

Literally, the term ion signifies a group of wandering atoms. An union is that group of atoms of an electrically decomposed or electro lyzed

Ani.]

[Ann.

molecule which appears at the anode. (See Electrolysis. Anode. )

As the anode is connected with the electro- positive terminal of a source, the anion is the electro-negative radical or group of atoms, and therefore appears at the electro-positive terminal.

A kathion, or electro-positive radical, appears at the kathode, which is connected with the electro-negative terminal of the battery. Oxygen and chlorine are anions. Hydrogen and the metals are kathions.

Anisotropic Conductor. — (See Conductor, Anisotropic?)

Anisotropic Medium. — (See Medium, Anisotropic?)

Annealing, Electric — — A process for annealing metals in which electric heating is substituted for ordinary heating.

Annual Inequality of Earth's Magnet- ism.— (See Inequality, Annual, of Earth's Magnetism.

Annual Variation of Magnetic Needle. — (See Needle, Magnetic, Annual Variation of.)

Annunciator, Burglar-Alarm An

annunciator used in connection with a system of burglar-alarms. (See Alarm, Burglar?)

Annunciator Clock, Electric — - — (See Clock, Electric Annunciator?)

Annunciator Drop. — (See Drop, Annun- ciator?)

Annunciator Drop, Automatic — (See Drop, Automatic Annunciator?)

Annunciator, Electro-Magnetic

An electric device for automatically indicating the points or places at which one or more electric contacts have been closed.

The character of the annunciator depends, of course, on the character of the places at which these points, places or stations are situated.

Annunciators are employed for a variety of purposes. In hotels they are used for indicating the number of a room the occupant of which desires some service, which he signifies by push- ing a button, thus closing an electric circuit. This is indicated or announced on the annuncia- tor by the falling of a drop, on which is printed a number corresponding with the room, and by the

ringing of a bell to notify the attendant. The num- ber is released by the movement of the armature of an electro-magnet. The drops are replaced in their former position by some mechanical device operated by the hand. In the place of a drop a

Fig. 14. Electro -Magnetic Annunciator.

needle is sometimes used, which, by the attraction of the armature of an electro-magnet, points to the number signaling.

Annunciators for houses, burglar-alarms, fire- alarms, elevators, etc., are of the same general con- struction.

Annunciators are general- ly operated by electro-mag- netic attraction or repulsion, and are therefore some- times called electro -magnetic annunciators.

Fig. 14 shows an annun- ciator suitable for use in hotels.

The numbers 28 and 85 are represented as having been dropped by the closing of the circuit connected with them.

Annunciator, Eleva- tor — An annuncia- tor connected with an elevator to indicate the floor signaling. One form of elevator annunciator is shown in Fig. 15.

Fig. z$. Elevator Annunciator.

Ann.]

23

[Ann.

Annunciator, Fire-Alarm An

annunciator used in connection with a system of fire-alarms. Annunciator, Gravity-Drop An

annunciator whose signals are operated by the fall of a drop.

Fig. ib. Gravity-Drop Annunciator.

A form of gravity-drop annunciator is shown in Fig. 16. The armature mechanism for the release of the drop will be understood by an in- spection of the drawing.

Annunciator, Hotel An annun- ciator connected with the different rooms of a hotel.

A hotel-annunciator is generally provided with a return bell and guest-call.

Annunciator, House An annun- ciator connected with the rooms of a house.

Annunciator, Needle An annun- ciator, the indications of which are given by the movements of a needle instead of the fall of a drop.

A form of needle-annunciator is shown in Fig. 17.

Annunciator, Oral or Speaking Tube

An annunciator electrically operated

by means of a puff of breath transmitted through an ordinary speaking tube.

The oral-annunciator is a contrivance whereby a central office is placed in communication with a number of speaking tubes coming from different points in a hotel or other place. A person in any room, who wishes to cpmmunicate with the central office, blows through the speaking tube in his room, and thus, by effecting an electric contact, rings a bell and operates a drop at the annunciator, thus indicat- ing the exact tube at which the attendant is to receive the message. The attendant can thus be placed in easy communication with each of the rooms whose speaking tubes connect with the annunciator.

Annunciator, Pendulum or Swinging — — An annunciator, the indicating arm of which consists of a pendulous.or swinging arm,

Fig. 77. Needle- Annunciator.

which, when at rest, points vertically down- ward, and which is moved to the right or left by the action of the current.

Pendulous, or swinging-annunciators are gen- erally so arranged as to need no replacement.

Ano.]

[App.

On the cessation of the current the indicator arm drops vertically downward.

A relay is preferably used with pendulum- annunciators, since the rapid makes and breaks of the current by the bell alarm interfere with their satisfactory action.

Anodal. — Pertaining to the anode. (See Anode)

Anodal Diffusion.— (See Diffusion,

Anode. — The conductor or plate of a de- composition cell connected with the positive terminal of a battery, or other electric source.

That terminal of an electric source out of which the current flows into the liquid of a decomposition cell or voltameter is called the anode.

That terminal of an electric source into which the current flows from a decomposition cell or voltameter is called the kathode.

The anode is connected with the carbon or positive terminal of a voltaic battery, and the kathode with the zinc, or negative terminal. Therefore the word anode has been used to signify the positive terminal of an electric source, and kathode, the negative terminal, and in this sense is employed generally in electro-thera- peutics. It is preferable, however, to restrict the use of the words anode and kathode to those terminals of a source at which electrolysis is taking place.

The terms anode and kathode in reality refer to the electro-receptive devices through which the current flows. Since it is assumed that the current flows out of a source from its positive pole or terminal, and back through the source at its negative pole or terminal, the pole of any device which is connected with the positive pole of a source is the part or place at which the current enters and flows through it, and that connected with the negative pole, the part at which it leaves. Hence, probably, the change in the use of the words already referred to.

Since the anion, or the electro-negative radical, appears at the anode, it is the anode of an electro- plating bath, or the plate connected with the positive terminal of the source, that is dissolved.

When the term anode was first proposed by Faraday, voltaic batteries were the only available electric source, and the term referred only to the

positive terminal of a voltaic battery when placed in an electrolyte.

Anodic. — Pertaining to the anode. (See Anode)

Anodic Electro-Diagnostic Reactions.—

(See Reactions, Kathodic and Anodic Elec- tro-Diagnostic?)

Anodic Opening Contraction.— (See Con- tration, Anodic Opening.)

Anomalous Magnet. — (See Magnet, An- omalous)

Anomalous Magnetization. — (See Mag- netization, Anomalous)

Anti-Induction Cable (See Cable,

Anti-Induction)

Anti-Induction Conductor. — (See Con- ductor, Anti-Induction)

Antilogous Pole.— (See Pole, Antilogous)

Anvil. — The front contact of a telegraphic key that limits its motion in one direction. (See Key, Telegraphic)

Aperiodic Galvanometer. — (See Galva- nometer, Aperiodic)

Apparatus, Faradic-Induction

An induction coil apparatus for producing faradic currents.

A voltaic battery is connected with the primary of an induction coil, and its current rapidly broken by an automatic break, or by a hand break. The alternating or faradic currents thus produced in the secondary coils are used for electro-therapeutic purposes. (See Coil, Induc- tion.)

Faradic-induction apparatus is made in a great variety of forms. They all operate, however, on essentially the same principles.

Apparatus, Faradic, Magneto-Electric

A small magneto-electric machine

employed in electro-therapeutics for producing faradic currents.

Magneto-electric faradic machines consist essen- tially of a coil of wire wrapped on an armature core that is rotated before the poles of permanent magnets. No commutator is employed, since it is desired to obtain rapidly alternating currents.

Apparatus, Interlocking — —Devices for mechanically operating from a distant signal

App.]

[Arc.

tower, railroad switches and semaphore signals for indicating the position of such switches, by means of a system of interlocking levers, so constructed that the signals and the switches are so interlocked as to render it impossible, after a route has once been set up and a signal given, to clear a signal for a route that would conflict with the one previ- ously set up. (See Block System for Rail- roads^)

Apparatus, Magneto-Electric Medical A term applied to small magneto- electric machines employed in medical elec- tricity for the production of uncommuted or faradic currents. (See Apparatus, Fara- dic, Magneto-Electric)

Apparatus, Registering-, Electric —

Devices for obtaining permanent records by electrical means.

Apparatus, Registering, Telegraphic

— A name sometimes given to a telegraphic recorder. (See Recorder, Chemical, Bain's, Recorder, Morse. Recorder, Siphon?)

Apparent Co-efficient of Induction. —

(See Induction, Apparent Co-efficient of.)

Arago's Disc. — (See Disc, Arago's)

Arc.— A voltaic arc. (See Arc, Voltaic)

Arc. — To form a voltaic arc.

A dynamo-electric machine is said to arc at the commutator, when the current passes as visible sparks across the spaces between adjacent seg- ments.

This action at the commutator is more gener- ally called sparking or burning.

Arc, Alternating A voltaic arc

formed by means of an alternating current.

In order to avoid the extinction of the arc a certain number of alternations per second is nec- essary. The alternating arc produces a loud singing noise. At very high frequencies, how- ever, the noise disappears.

The alternating arc, not possessing a fixed posi- tive crater, requires to be covered by a good reflector to throw the light downward.

Arc, Ampe're A single conductor

bent in an arc of a circle, and used in electric balances for measuring the electric current.

Arc Blow-Pipe.— (See Blow-Pipe, Elec- tric Arc.}

Arc, Compound An arc formed

between more than two separate electrodes.

Arc, Counter Electromotiye Force of

An electromotive force generally be- lieved to be set up on the formation of a voltaic arc, opposed in direction to the electro- motive force maintaining the arc. (See Force, Electromotive, Counter?)

This counter electromotive force is believed to have its origin partly in the energy absorbed at the crater of the positive carbon, where the car- bon is volatilized, and given out at the nipple on the negative carbon, where it is deposited or solidified. It is to be noted in this connection that the apparent resistance of the carbon voltaic arc is not directly proportional to the length of the arc.

Arc, Electric A term sometimes

used for the voltaic arc. (See Arc, Voltaic)

Arc, Frying of — — A frying sound at- tending the formation of a voltaic arc when the carbons are too near together.

The cause of the frying sound is probably the same as that of hissing. (See Arc, Hissing of '.)

Arc, Hissing of A hissing sound

attending the formation of voltaic arcs when the carbons are too near together.

The cause of the hissing is not entirely under- stood. Prof. Elihu Thomson suggests that it is due to a too rapid volatilization of the carbons.

Arc Lamp. — (See Lamp, Arc)

Arc Lamp, Electric (See Lamp,

Electric Arc)

Arc Lamp, Triple Carbon Electric

—(See Lamp, Arc, Triple Carbon Electric)

Arc Lighting. — (See Lighting, Arc)

Arc, Metallic A voltaic arc formed

between metallic electrodes.

When the voltaic arc is formed between metallic electrodes instead of carbon electrodes, a flaming arc is obtained, the color of which is characteristic of the burning metal ; thus copper forms a brill- iant green arc. The metallic arc, as a rule is much longer than an arc with the same current taken between carbon electrodes.

Arc Micrometer. — (See Micrometer, Arc)

Arc.]

[Arc.

Arc, Noisy A voltaic arc, the

maintenance of which is attended by frying, hissing, or spluttering sounds.

Arc, (Juiet A voltaic arc which is

maintained without sensible sounds.

Arc, Roaring of — • — A roaring sound attending the formation of a voltaic arc when the carbons are too near together and a very powt rf ul current is used.

Arc, Simple An arc formed be- tween two electrodes.

Arc, Spluttering of A spluttering

sound attending the formation of a voltaic arc.

Prof/Elihu Thomson suggests that the cause of spluttering is due to the presence of impurities in the carbons, or from the sudden evolution of gas from insufficiently baked carbons.

Arc, Yoltaic — —The brilliant arc or bow of light which appears between the elec- trodes or terminals, generally of carbon, of a sufficiently powerful source of electricity, when separated a short distance from each other.

The source of light of the electric arc lamp.

It is called the voltaic arc because it was first obtained by the use of the battery invented by Volta. The term arc was given to it from the shape of the luminous bow or arc formed between the carbons.

To form the voltaic arc the carbon electrodes are first placed in contact and then gradually separated. A brilliant arc of flame is formed be- tween them, which consists mainly of volatilized carbon. The electrodes are consumed, first, by actual combination with the oxygen of the air; and, second, by volatilization under the combined influence of the electric current and the intense heat.

As a result of the formation of the arc, a crater is formed at the end of the positive carbon, and appears to mark the point out of which the greater part of the current flows.

The crater is due to the greater volatilization of the electrode at this point than elsewhere. It marks the position of highest temperature of the electrodes, and is the main source of the light of the arc. When, therefore, the voltaic arc is em- ployed for the purposes of illumination with vertically opposed carbons, the positive carbon should be made the upper carbon, so that the

focus of greatest intensity of the light may be favorably situated for illumination of the space below the lamp. When, however, it is desired to illumine the side of a building above an arc lamp, the lower carbon should be made positive.

The positive carbon is consumed about twice as rapidly as the negative, both because the negative oxygen attacks the points of the positive carbon. ' and because the positive carbon suffers the most rapid volatilization.

The electric current passes through the space occupied by the voltaic arc because—

(I.) The heated arc is a partial conductor of electricity.

(2.) Because small charges of electricity are carried bodily forward from the positive to the negative carbon through the space of the voltaic arc, by means of the minute particles which are volatilized at the positive electrode.

S. P. Thompson has shown that the tempera- ture of the light-emitting surface of the carbon is the temperature of the volatilization of carbon, and is therefore constant/

Dr. Fleming found that " A rise of potential along the arc takes place very suddenly, just in the neighbor- hood of the crater. ' '

The crater in the end of the positive car- bon is seen in Fig. 18. On the opposed end of the negative carbon a projection or nipple is formed by the de- posit of the electrical- ly volatilized carbon. Fig. r8. Voltaic Arc. The rounded masses or globules that appear on the surface of the elec- trodes are due to deposits of molten foreign mat- ters in the carbon.

The carbon, both of the crater and its opposed nipple, is converted into pure, soft graphite.

Arc, Voltaic, Resistance of— —The resistance offered by the voltaic arc to the passage of the current.

As in all other conductors, the ohmic resistance of the arc increases with its length, and decreases with its area of cross-section. The apparent resistance, however, is not directly proportional to the length. An increase of temperature de- creases the resistance of the voltaic arc.

Arc.]

[Arm.

The total apparent resistance of the voltaic arc is composed of two parts, viz. :

(I.) The true ohmic resistance. (See Resist- ance, Ohtnic.)

(z.) The counter electromotive force, or spuri- ous resistance. (See Resistance, Spurious.)

Arc, Watt A voltaic arc, the elec- tric power of which is equal to a given number of watts.

The ordinary long-arc, as employed in arc lighting, has a difference of potential of about 45 volts and a current strength of about 10 amperes. It is, therefore, a 45O-watt arc.

Arch, Auroral The archlike form

sometimes assumed by the auroral light. (See Aurora Borealis?)

Arcing. — Discharging by means of voltaic arcs. (See Arc, Voltaic?)

Arcing at the commutator of a dynamo-electric machine not only prevents the proper operation of the machine, but eventually leads to the de- struction of the brushes and the commutator.

Areometer, Bead — A form of are- ometer suitable for rapidly testing the density of the liquid in a storage cell.

The bead areometer consists of a glass tube, open at both top and bottom, containing a few glass beads, so weighted as to float at liquid densities such as 1.105, 1.170, 1.190 and 1. 200. To use the instrument, it is immersed in the liquid of the storage cell, and then withdrawn. The finger being kept in the upper opening, the liquid does not escape through the small opening at the bottom. The density is then ascer- tained by noting the beads that float.

Areometer or Hydrometer. — An instrument for determin- ing the specific gravity of a liquid.

A common form of hydrometer consists, as shown in Fig. 19, of a closed glass tube, provided with a bulb, and filled at the lower end V

with mercury or shot, so as to in- ®

sure its vertical position when Fig. 19. Hy- floating in a liquid. When placed drometer. in different liquids, it floats with part of the tube out of the liquid. The lighter the liquid, the 2— Vol. 1

smaller is the portion that remains out of the liquid when the instrument floats. The specific gravity is determined by observing the depth to which the instrument sinks when placed in different liquids, as compared with the depth it sinks when placed in water.

Areometry. — The measurement of specific gravity by means of an areometer.

Argand Burner, Electric Hand-Lighter -(See Burner, Argand, Electric Hand- Lighter?)

Argand Burner, Electric Plain-Pendant — (See Burner, Plain Pendant, Argand, Electric?)

Argand Burner, Electric Ratchet-Pen- dant — —(See Burner, Ratchet-Pendant, Argand) Electric?)

Argyrometry. — The art of determining the weight of electrolytically deposited silver. (See Balance, Plating?)

Arm, Balance One of the resist- ances of an electric balance. (See Arms, Bridge or Balance. Bridge, Electric?)

Arm, Bridge — — A bridge arm. (See Arms, Bridge or Balance?)

Arm, Cross — — A horizontal beam at- tached to a pole for the support of the in- sulators for telegraph, electric light or 'other electric wires.

A telegraphic arm. (See Arm, Tele- graphic?)

Arm, Rocker — An arm on which the

brushes of a dynamo or motor are mounted for the purpose of shifting their position on the commutator.

Arm, Semaphore The movable

arm of the signal apparatus employed in block systems for railroads, for the purpose of in- forming engineers of trains of the condition of the road as regards other trains.

In the absolute block system, as used on some roads, there are two positions for the semaphore arm, viz. :

(i.) For Danger — when in a horizontal position,, or at 90 degrees with the vertical supporting pole.

(2. ) Clear — when dropped below the horizontal position through an angle of 75 degrees.

In the Permissive Block System, a third position

Arm.]

[Arm.

intermediate between the ist and the zd, or at an angle of 37 degrees 30 minutes with the horizontal position, is used for caution. (See Block System for Railroads. ,)

Arm, Signal A semaphore arm.

(See Arm, Semaphored)

Arm, Telegraphic — —A cross-arm placed on a telegraphic pole for the support of the insulators.

These arms are generally called cross-arms.

Armature. — A mass of iron or other magnetizable material placed on or near the pole or poles of a magnet.

In the case of a permanent magnet, the arma- ture, when used as a keeper, is of soft iron and is placed directly on the magnet poles. In this case it preserves or keeps the magnetism by closing the lines of magnetic jorce of the magnet through the soft iron of the armature, and is then called a keeper. (See Force, Magnetic, Lines of.}

In the case of an electro-magnet, the armature is placed near the poles, and is moved toward them whenever the magnet is energized by the passage of the current through the magnetizing coils. This movement is made against the action of a spring or weights, so that on the loss of magnetism by the magnet, the armature moves from the magnet poles. (See Magnet, Permanent. Magnet, Keeper of .}

When the armature is of soft iron it moves to- ward the magnet on the completion of the circuit through its coils, no matter in what direction the current flows, and is then called a non-polar- ized armature. (See Armature, Non-Polarized. )

When made of steel, or of another electro-mag -

Fig.2O. Bi-polar Armature.

net, it moves from or toward the poles, accord- ing to whether the poles of the armature are of the same or of a different polarity from those of the magnet. Such an armature is called a polarized armature. (Set Armature, Polarized.)

Armature, Bi-polar An armature

of a dynamo-electric machine the polarity of which is reversed twice in every revolution through the field of the machine.

A form of bi-polar armature is shown in Fig. 20. The word bi-polar armature is not generally employed. The term applies rather to the field- magnet poles than to the armature.

Armature Bore. — (See Bore, Armature.}

Armature Bore, Elliptical — —(See Bore, Elliptical Armature?)

Armature Chamber. — (See Chamber, Armature?)

Armature Coils, Dynamo - — (See Coils, Armature, of Dynamo-Electric Ma- chine?)

Armature Core, Dynamo - — (See Core, Armature, of Dynamo-Electric Ma- chine?)

Armature, Cylindrical — — A term sometimes applied to a drum armature. (See Armature, Drum. Armature, Dy- namo-Electric Machine?)

Armature, Cylindrical Ring.— A ring armature with a core in the shape of a com- paratively long cylinder.

Armature, Disc An armature of a

dynamo-electric machine, in which the arma- ture coils consist of flat coils, supported on the surface of a disc. (See Armature, Dy- namo-Electric Machine?)

Armature, Dissymmetrical Induction of

— Any induction produced in the arma- ture of a dynamo-electric machine that is un- equal in amount on opposite halves, or in sym- metrically disposed portions of the armature.

Dissymmetrical induction in the armature may cause annoying or injurious sparking at the com- mutator. It may arise —

(i.) From a lack of symmetry in the amount of the armature windings.

(2.) From a lack of symmetry in the arrange- ment of the armature windings on the armature core.

(3. ) From a lack of symmetry of the pole pieces of the machine.

(4.) From an improper position of the brushes

Aroi.]

29

[Arm,

as regards the neutral point on the commutator, causing a temporary short-circuiting of one or more of the armature coils.

Armature, Drum — — An armature of a dynamo-electric machine, in which the armature coils are wound longitudinally over the surface of a cylinder or drum. (See Armature, Dynamo-Electric Machine?)

A form of drum-armature is shown in Fig. 21.

Fig. 21. Drum- Armature.

Armature, Dynamo-Electric Machine

The coils of insulated wire together

with the iron armature core, on or around which the coils are wound.

That part of a dynamo-electric machine in which the differences of potential which cause the useful currents are generated.

Generally, that portion of a dynamo-elec- tric machine which is revolved between the pole pieces of the field magnets.

The armature of a dynamo-electric machine usually consists of a series of coils of insulated wire or conductors, wrapped around or grouped on a central core of iron. The movement of these wires or conductors through the magnetic field of the machine produces an electric cur- rent by means of the electromotive forces so gen- erated. Sometimes the field is rotated ; some- times both armature and field rotate.

The armatures of dynamo-electric machines are of a great variety of forms. They may for convenience be arranged under the following heads, viz.:

Cylindrical or drum-armatures, disc-arma- tures, pole or-radial armatures, ring armatures, and spherical- armatures . For further particulars see above terms. Armatures are also divided

into classes according to the character of fee magnetic field through which they move — viz.: unipolar, bipolar, and multipolar- armatures.

The English sometimes use the word cylindrical armature as a synonym of ring-armature.

A unipolar-armature is one whose polarity is never reversed. A bipolar-armature is one in which the polarity is reversed twice in every rotation; multipolar armatures have their po- larity reversed a number of times in every rota- tion.

The term armature as applied to a dynamo- electric machine was derived from the fact that the iron core acts to magnetically connect the two poles of the field magnets in the same manner that an ordinary armature connects the poles of a magnet.

Armature, Flat Ring — —A ring-arma- ture with a core in the shape of a short cylin- drical ring.

Armature, Girder — — An armature

with an H -shaped or girder-like core.

An H -shaped armature.

Armature, Intensity — —An old term for an armature with coils of many turns and of a comparatively high resistance.

Armature, Lamination of Core of — — A division of the iron core of the armature of a dynamo-electric machine or motor, so as to avoid the formation of eddy-currents therein. (See Core, Lamination of. Cur- rents, Eddy.)

Armature, Mnltipolar — —A dynamo- electric machine armature whose polarity is reversed more than twice during each rotation in the field of the machine.

Armature, Neutral A non-polarized

armature. (See Armature, Non-Polarized.)

Armature, Neutral-Relay A relay

armature, consisting of a piece of soft iron, which closes a local circuit whenever its elec- tro-magnet receives an impulse over the main line. (See Artnature, Polarized?)

This term is applied in contradistinction to a polarized relay armature.

Armature, Non-Polarized — An

armature of soft iron, which is attracted toward the poles of an electro-magnet on the comple

Arm.]

30

[Arm.

tion of the circuit, no matter in what direc- tion the current passes through the coils.

The term non-polarized is used in contradistinc- tion to polarized armature. (See Armature, Polarized.}

Th. non-polarized armature of a relay magnet is generally called the neutral -relay armature.

Armature of a Cable, or Cable-Armature.

— A term sometimes employed for the sheath- ing or protecting coat of a cable.

The term armor sheathing or coating is prefer- able.

Armature of a Condenser, or Condenser Armature. — A term sometimes applied to the metallic plates of a condenser or Leyden jar.

The use of this term is unnecessary and ill- advised. The term coating or plate would appear to be preferable.

Armature of Holtz Machine, or Holtz- Machine Armature. — The pieces of paper that are placed on the stationary plate of the Holtz and other similar electrostatic induction machines.

Armature Pockets.— (See Pockets, Arma- ture)

Armature, Polarized An armature

which possesses a polarity independent of that imparted by the magnet pole near which it is placed.

In permanent magnets the armatures are made of soft iron, and therefore, by induction, become of a polarity opposite to that ol the magnet poles that lie nearest them. They have, therefore, only a motion of attraction toward such pales. (See Induction, Magnetic. )

In electro-magnets the armatures may either be made of soft iron, in which case they are attracted only on the passage of the current; or they may be formed of permanent steel magnets, or may be electro-magnets themsehes, in which case the pas- sage of the current through the coils of the elec- tro-magnet, or electro-magnets, may cause either attraction or repulsion, according as the adjacent poles are of opposite polarity or are of the same polarity.

Armature, Pole — — An armature the coils of which are wound on separate poles

that project radially from the periphery of a disc, drum or ring. A pole-armature showing the arrangement of

Fig. Z2. Pole- Armature.

the coils and their connection to the commutator segments is seen in Fig. 22.

Armature, Quantity An old term

for an armature wound with but a few coils of comparatively low resistance.

Armature, Radial — — A term some- times used instead of pole-armature. (See Armature, Pole.)

Armature, Ring A dynamo-electric

machine armature, the coils of which are wound on a ring-shaped core. c

Fig- 23- Ring-Armature.

A ring-armature is shown in Fig. 23, together with the disposition of the coils and their connec- tion to the segments of the commutator.

Armature, Shuttle A variety of

drum armature in which a single coil of wire is wound in an H -shaped groove formed in a bobbin shaped core.

The old form of Siemens-armature.

Armature, Single-Loop A closed

conducting circuit consisting of a single loop, capable of revolving in a magnetic field so as to cut its lines of force.

Armature, Spider. — (See Spider, Arma- ture)

Arm.]

31

Arr.

Armature, Spherical A dynamo- electric machine armature, the coils of which are wound on a spherical iron core.

The Thomson- Houston dynamo, which is the only machine employing an armature of this type, has its armature formed by wrapping three coils of insulated wire on a core of iron so shaped as to insure an approximately spherical armature when wrapped.

Armature, Toothed-Ring — — An ar- mature, the core of which is in the shape of a ring, provided with a number of teeth in the spaces between which the armature coils are placed.

Armature, Unipolar — — A dynamo- electric machine armature whose polarity is not reversed during its rotation in the field of the machine.

Armature, Ventilation of — — A pro- cess for insuring the free passage of air through the armature of a dynamo-electric machine in order to prevent overheating.

Armor of Cable. — (See Cable, Armor of.)

Armored Cable. — (See Cable, Armored?)

Armored Conductor. — (See Conductor, Armored!)

Arms, Bridge or Balance — — The electric resistances, in the electric balance or bridge. (See Bridge, Electric!)

Zn C Fig. 24. Arms of Balance.

An unknown resistance, such, for example, as D, Fig. 24, is measured by proportioning the known resistances, A, C and B, so that no current flows through the galvanometer G, across the circuit or bridge M G N.

Arms, Proportionate The two re- sistances or arms of an electric bridge whose relative or proportionate resistances only are required to be known in order to determine,

in connection with a known resistance, the value of an unknown resistance placed in the remaining arm of the bridge.

Thus is Fig. 24, A and B, are the proportionate arms.

Arrangement or Deyice, Electromotive

A term sometimes employed to rep- resent a dynamo-electric machine, voltaic cell or other electric source, by means of which electromotive force can be produced.

Electric sources do not produce electric cur- rents, but differences of potential or electro- motive force. Electric sources are therefore very properly termed electromotive devices.

Arrester, Lightning — — A device by means of which the apparatus placed in any electric circuit is protected from the destruc- tive effects of a flash or bolt of lightning.

In the phenomena of lateral induction and alternative path, we have seen the tendency of a disruptive discharge to take a short-cut across an intervening air space, rather than through a longer though better conducting path. Most lightning arresters are dependent for their opera- tion on this tendency to lateral discharge. (See Induction, Lateral. Path, Alternative.}

A form of lightning arrester is shown in Fig. 25.

Fig. 23- Comb Lightning- Arrester.

The line wires, A and B, are connected by two metallic plates to C and D, respectively.

These plates are provided with points, as shown, and placed near a third plate, connected to the ground by the wire G. Should a bolt strike the line, it is discharged to the .earth through the wire G.

Various forms are given to lightning arresters of this type. The projections are sometimes placed on the ground-connected plate as well as on the plates connected to line wires. This form is sometimes called a comb arrester, or protector.

Arr.]

[Ast.

Arrester, Lightning, Comb - —A

term sometimes applied to a lightning ar- rester in which both the line and ground plates are furnished with a series of teeth, like those on a comb. (See Arrester, Light- ning)

Arrester, Lightning, Counter-Electro- motive Force — — A lightning arrester, in which the passage of the discharge through the instruments to be protected is opposed by a counter-electromotive force, generated by induction on the passage of the discharge of the bolt to earth.

The counter-electromotive force lightning ar- rester is an invention of Professor Elihu Thomson.

It assumes a variety of forms. In the shape shown in Fig. 26, the line circuit of the dynamo,

Fig. 26. Counter-Electromotive Force Lightning Arrester.

D, has one end connected to ground, and the other end has two conducting paths to ground. One of these paths is through the ordinary comb- protector at P, by the ground plate E; this cir- cuit includes a few turns of wire C'. The other path is through a corres- ponding coil C, either interior or exterior to C', so as to be within its in- ductive field. As will be [ E I seen from the figure, C, is

Fig. 27. Counttr-Elec- connected through the tromotive force Light- machine to the ground. ning Arrester. The induction coils C

and C', are thoroughly insulated from each other.

Should a lightning flash or other static discharge pass through the circuit C', which is of compara- tively low self-induction, a counter-electromotive force is produced in the other coil C, which protects the line circuit.

In the form of lightning arrester shown in Fig. 27, the coil in the path of the direct light- ning discharge is formed into an exterior mesh or net work surrounding the dynamo to be pro- tected. In this case, the coils of the dynamo act as the secondary coils in which the counter elec- tromotive force is set up.

Arrester, Lightning, Transformer

— A form of lightning arrester designed for the protection of transformers.

The Thomson arrester for transformers oper- ates on the same principle as his arc-line pro- tector. In the latter the arc, when formed, is blown out by the action of the field of an electro-magnet. This arc is formed on curved metallic bows, one of which is connected to line and the other to earth. The arc is formed at the smallest interval between the bows, and is extin- guished by being driven by action of a magnetic field toward greatest interval.

Arrester Plate of Lightning Protector.— (See Plate, Arrester, of Lightning Pro- tector^

Arrester Plates. — (See Plates, Arrester^

Articulate Speech. — (See Speech, Articu- lated,

Artificial Carbons.— (See Carbons, Arti- ficial^

Artificial Illumination.— (See Illumina- tion, Artificial.}

Artificial Line.— (See Line, Artificial.}

Artificial Magnet— (See Magnet, Arti- ficial.}

Asphyxia. — Suspended respiration, result- ing eventually in death, from non-aeration of the blood.

In cases of insensibility by an electric shock a species of asphyxia is sometimes brought about. This is due, probably, to the failure of the nerves and muscles that carry on respiration. The exact manner in which death by electrical shock results is not known. (See Death, Electric. }

Assy m metrical Resistance. — (See Resist- ance, Assymmetrical.)

Astatic. — Possessing no directive power.

Usually applied to a magnetic or electro-mag- netic-device which is free from any tendency to take a definite position on account of the earth's magnetism.

Ast,]

[Ato.

Astatic Circuit.— (See Circuit, Astatic}

Astatic Couple.— See Couple, Astatic.}

Astatic Galvanometer. — (See Galvanom- ster, Astatic.)

Astatic Needle.— (See Needle, Astatic.}

Astatic Pair.— (See Pair, Astatic}

Astatic System.— (See System, Astatic}

Astronomical Meridian. — (See Meridian, Astronomical}

Asymptote of Curve. — (See Curve, Asymp- tote of}

Atmosphere, An A unit of gas or

fluid pressure equal to about 1 5 pounds to the square inch.

At the level of the sea the atmosphere exerts a pressure of about 15 pounds avoirdupois, or, more accurately, 14.73 pounds, on every square inch of the earth's surface. This value has there- fore been taken as a unit of fluid pressure.

For more accurate measurements pounds to the square inch are employed.

In the metric system of weights and measures an atmosphere is considered equal to 1,033 grammes per square centimetre.

Atmospheric pressures are measured by instru- ments called Manometers. (See Manometer.)

Atmosphere, Residual The traces

of air or other gas remaining in a space which has been exhausted of its gaseous contents by a pump or other means.

It is next to impossible to remove all traces of air from a vessel by any known form of pump or other appliance. (See Vacuum, Absolute.)

Atmosphere, The — The ocean of

.air which surrounds the earth.

The atmosphere is, approximately, composed, by weight, of oxygen 23 parts, and nitrogen 77 parts. Besides these there are from 4 to 6 parts in 10,000 of carbonic acid gas (or about a cubic inch of carbonic acid to a cubic foot of air), and varying proportions of the vapor of water.

The oxygen, nitrogen and carbonic acid form the constant ingredients of the atmosphere, the vapor of water the variable ingredient. There are in most localities a number of other variable ingredients present as impurities.

Atmospheric Electricity. — (See Electric- ity, Atmospheric.)

Atmospheric Electricity, Origin of

— (See Electricity, Atmospheric, Origin of.)

Atom. — The smallest quantity of elemen- tary or simple matter that can exist.

An ultimate particle of matter.

Atom means that which cannot be cut. It is generally believed that material atoms are abso- lutely unalterable in size, shape, weight and den- sity ; that they can neither be cut, scratched, flattened, nor distorted ; and that they are un- affected in size, density, or shape, by heat or cold, or by any known physical force.

Although almost inconceivably small, atoms nevertheless possess a definite size and mass. According to Sir William Thomson, the smallest visible organic particle, 1-4000 of a millimetre in diameter, will contain about 30,000,000 atoms.

Atom, Closed-Magnetic Circuit of —

(See Circuit, Closed-Magnetic, of Atom}

Atom, Gramme - — Such a number of grammes of any elementary substance as is numerically equal to the atomic weight of the substance.

The gramme-atom of a substance represents the number of calories required to raise the tem- perature of one gramme of that substance through I degree C. (See Heat, Atomic. Calorie.) Thus, in the case of chlorine, whose atomic weight is 35.5, its gramme-atom is 35.5 ; consequently 35.5 small calories of heat would be required to raise one gramme-atom of chlorine through i degree C.

Atom of Electricity.— (See Electricity, Atom of}

Atom, Vortex A number of particles

of the universal ether moving in the manner of a vortex ring.

The theory of vortex atoms, so formed from vortex rings, was propounded by Sir William Thomson in order to explain how a readily mov- able substance, like the universal ether, could be made to possess the properties of a rigid solid. If it be granted that a vortex motion has once been imparted to the universal ether, Thomson shows that such rings would be indestructible. (See Matter, Thomson's Hypothesis of.)

Atomic Attraction. — (See Attraction, Atomic}

Ato.]

34

[All.

Atomic Capacity. — (See Capacity, Atom- ic)

Atomic Currents. — (See Currents, Atom- ic)

Atomic Energy. — (See Energy, Atomic) Atomic Heat— (See Heat, Atomic)

Atomic or Molecular Induced Currents.

— (See Currents, Induced, Molecular or Atomic) Atomic Weight.— (See Weight, Atomic)

Atomicity. — The combining capacity of the atoms.

The relative equivalence of the atoms or their atomic capacity.

The elementary atoms do not always combine atom for atom. Some single atoms of certain elements will combine with two, three, four, or even more atoms of another element.

The value of the atomic capacity of an atom is also called its quantivalence or valency. Elements whose atomic capacity is —

One, are called Monads, or Univalent. Two, " Dyads, " Bivalent.

Three, " Triads, " Trivalent.

Four, " Tetrads, " Quadrivalent.

Five, " Pentads, " Quinquivalent

Six, " Hexads, " Sexivalent.

Seven, " Heptads, " Septivalent.

Atomization. — The act of obtaining liquids in a spray of finely divided particles.

In most cases the term is not literally correct, as each of the smallest particles so obtained usu- ally consist of many thousands of atoms.

Atomize. — To separate into a fine spray by means of an atomizer. (See Atomizer)

Atomizer. — An apparatus for readily ob- taining a finely divided jet or spray of liquid.

A jet of steam, or a blast of air, is driven across the open end of a tube that dips below the surface of the liquid to be atomized. The partial vacuum so formed draws tip the liquid, which is then blown by the current into a fine spray.

Attract. — To draw together. Attracted-Disc Electrometer.— (See Elec- trometer, Attracted-Disc)

Attract ins?. — Drawing together.

Attraction.— Literally the act of drawing together.

In science the name attraction is given to a series of unknown causes which effect, or are as- sumed to effect, the drawing together of atoms, molecules or masses.

Attraction and repulsion underlie nearly all natural phenomena. While their effects are well known, it is doubtful if anything is definitely known of their true causes.

Since attraction, pure and simple, necessitates the belief in action at a distance, an action which is now generally discredited, we must, strictly speaking, regard the term attraction as being but a convenient substitution of the effect for the cause.

It would appear much more reasonable to re- gard the effects of attraction as produced by a true push exerted from the outside of the bodies. According to this notion, two masses of matter undergoing attraction are pushed together rather than drawn or attracted together.

It has been suggested that gravitation may per- haps be an effect of a longitudinal motion or vibra- tory thrust in the universal ether. If this is the case, and the ether is sensibly incompressible, the velocity of gravitation, it would appear, should be almost infinite.

Attraction, Atomic — —The attraction which causes the atoms to combine. (See Affinity, Chemical)

In the opinion of Lodge, atomic attraction is the result of the attraction of dissimilar charges of electricity possessed by all atoms, which are capa - ble of uniting or entering into chemical combi- nation. (See Electricity, Atom of)

Attraction, Capillary — —The molec- ular attractions that are concerned in capillary phenomena. (See Capillarity)

Attraction, Electro-Dynamic — —The mutual attraction of electric currents, or of conductors through which electric currents are passing. (See Dynamics, Electro)

Attraction, Electro-Magnetic — —The mutual attraction of the unlike poles of electro-magnets. (See Magnet, Electro.}

Attraction, Electrostatic - —The mutual attraction exerted between unlike electric charges, or bodies possessing unlike o'ectric charges.

Alt.]

35

[Aur.

For example, the pith ball supported on an in- sulated string is attracted, as shown at A, Fig. 28,

Fig. 28. Electrostati Attraction.

Fig: 29. Electrostati Repulsion.

by a bit of sulphur which has been briskly rubbed by a piece of silk. As soon, however, as the ball touches the sulphur and receives a charge, it is repelled, as shown at B, Fig. 29.

These attractions ai d repulsions are due to the effects of electrostatic induction. (See Induction, Electrostatic.}

Attraction, Magnetic — — The mutual attraction exerted between unlike magnet poles.

Magnetic attractions and repulsions are best shown by means of the magnetic needle N S, Fig. 30. The N. pole of an approached magnet

Fig. 30. Magnetic Attraction.

attracts the S. pole of the needle but repels the N. pole.

The laws of magnetic attraction and repulsion may be stated as follows, viz.:

(i ) Magnet poles of the same name repel each other; thus, a north pole repels another north pole, a south pole repels another south pole.

Fig. 31. floating Magnet.

(2.) Magnet poles of unlike names attract each other; thus a north pole attracts a south pole, or a south pole attracts a north pole.

A small bar magnet, N S, Fig. 31, laid on the top of a light vessel floating on the surface of a liquid, may be readily employed to illustrate the laws of magnetic attraction and repulsion.

Attraction, Mass — —The mutual at- traction exerted between masses of matter. (See Gravitation}

Attraction, Molar A term some- times employed for mass attraction.

Gravitation is an example of mass attraction, where the mass of the earth attracts the mass of some body placed near it. (See Gravitation.}

Attraction, Molecular The mutual

attraction exerted between neighboring molecules.

The attraction of like molecules, or those of the same kind of matter, is called Cohesion ; that of unlike molecules, Adhesion.

The tensile strength of iron or steel is due to the cohesion of its molecules. Paint adheres to wood, or ink to paper, by cohesion or the attrac- tion between the unlike molecules.

Attraction of Grayitation. — A term gen- erally applied to the mutual attraction be- tween masses. (See Gravitation^)

Attractions and Repulsions of Currents. — (See Currents, Attractions and Repulsions of}

Audiphone. — A thin plate of hard rubber held in contact with the teeth, and maintained at a certain tension by strings attached to one of its edges, for the purpose of aiding the hearing.

The plate is so held that the sound-waves from a speaker's voice impinge directly against its flat surface. It operates by means of some of the waves being transmitted , to the ear directly through the bones of the head.

The audiphone is sometimes called a denti- phone.

Aural Electrode. — (See Electrode, Aural}

Aurora Australis. — The Southern Light.

A name given to an appearance in the south-

Aur.]

[Aut.

ern heavens similar to that of the Aurora Borealis. (See Aurora Borealis.}

Aurora Borealis. — The Northern Light.

Luminous sheets, columns, arches, or pillars of pale, flashing light, generally of a red color, seen in the northern heavens.

The auroral light assumes a great variety of ap- pearances, to which the terms auroral arch, bands, cor once, curtains and streamers are applied.

The exact cause of the aurora is not as yet known. It would appear, however, beyond any reasonable doubt, that the auroral flashes are due to the passage of electrical discharges through the upper, and therefore rarer, regions of the atmos- phere. The intermittent flashes of light are prob- ably due to the discharges being influenced by the earth's magnetism.

Auroras are frequently accompanied by mag- netic storms. (See Storm, Magnetic. )

The occurrence of auroras is nearly always simultaneous with that of an unusual number of sun spots. Auroras are therefore probably con- nected with outbursts of the solar energy. (See Spots, Sun.)

The auroral light examined by the spectroscope gives a spectrum characteristic of luminous gaseous matter, i. e., contains a few bright lines; but, ac- cording to S. P. Thompson, this spectrum is pro- duced by matter that is not referable with cer- tainty to that of any known substance.

Whatever may be the exact cause of auroras, their appearance is almost exactly reproduced by the passage of electric discharges through vacua.

Aurora Polaris. — A general term some- times applied to aurora in the neighborhood of either pole, or in either the northern or the southern hemisphere.

Auroral Arch. — (See Arch, Auroral?)

Auroral Bands. — (See Bands, Auroral}

Auroral Coronse. — (See Corona, Au- roral?)

Auroral Curtain. — (See Curtain, Au- roral.}

Auroral Flashes. — (See Flashes, Auroral.}

Auroral Light — (See Light, Auroral?)

Auroral Storm.— (See Storm, Auroral}

Auroral Streamer. — (See Streamer, Au- roral}

Auroras and Magnetic Storms, Peri-

odicity of Observed coincidences be- tween the occurrence of auroras, magnetic storms, and sun-spots.

The occurrence of auroras, or magnetic storms, at periods of about eleven years apart, corre- sponds to the well-known eleven-year sun-spot period.

The period also agrees with a variation in the magnetic declination of any place, which, accord- ing to Sabine, occurs once in every eleven years.

Austral Magnetic Pole.— (See Pole, Mag- netic, Austral}

Autographic Telegraphy. — (See Teleg- raphy, Autographic}

Automatic Annunciator Drop. — (See Drop, Annunciator, Automatic}

Automatic Bell.— , See Bell, Automatic Electric}

Automatic Contact Breaker.— (See Con- tact Breaker, Automatic}

Automatic Cut-Out.— (See Cut-Out, Au- tomatic}

Automatic Cut-Out for Multiple-Connect- ed Electro-Receptive Devices. — (See Cut- Out, Automatic, for Multiple-Connected Electro-Receptive Devices}

Automatic Cut-Out for Series-Connected Electro-Receptive Devices. —(See Cut-Out, Automatic , for Series-Connected Electro-Re- ceptive Devices}

Automatic Drop. — (See Drop, Auto- matic}

Automatic Electric Burner. — (See Burn- er, Automatic Electric}

Automatic Electric Safety System for Railroads. — (See Railroads, Automatic Elec- tric Safety System for}

Automatic Fire-Alarm. — (See Alarm, Fire, Automatic}

Automatic Gas Cut-Off. — (See Cut-Off, Automatic Gas}

Automatic Indicator. — (See Indicator, Automatic}

Automatic Make-and-Break.— (See Make- and-Break, Automatic}

Automatic Oiler. — (See Oiler, Automatic.

Aut.]

37

[B. A, U.

Automatic Paper-Winder. — (See Winder, Telegraphic Paper.}

Automatic Regulation. — (See Regulation, Automatic.)

Automatic Regulator. — (See Regulator, Automatic?)

Automatic Search-Light. — (See Light, Search, Automatic?)

Automatic Switch for Incandescent Elec- tric Lamp. — (See Switch, Automatic, for Incandescent Electric Lamp?)

Automatic Telegraphy. — (S e e Teleg- raphy, Automatic?)

Automatic Telephone Switch. — (See Switch, Telephone, Automatic?)

Automatic Time Cut-Outs.— (See Cut- Out, Automatic Time?)

Automatic Variable Resistance.— (See Resistance, Variable, Automatic?)

Automatically Regulable. — (See Regula- ble, Automatically?)

Automobile Torpedo.— (See Torpedo, Au- tomobile?)

Average or Mean Electromotive Force. — (See Force, Electromotive, Average, or Mean?)

Axes of Co-ordinates. — (See Co-ordinates, Axes of?)

Axial Magnet.— (See Magnet, Axial?)

Axis, Magnetic The line around

which a magnetic needle, free to move, but which has come to rest in a magnetic field, can be turned without changing the set or direction in which it has come to rest.

Axis, Magnetic, of a Straight Needle

— A straight line drawn through the magnet, joining its poles.

The magnetic axis of a straight needle may be regarded as a straight line passing through the poles of the needle and its point of support.

The magnetic axis may not correspond with the geometric axis of the needle. This leads to an error in reading the true direction in which the needle is pointing, which must be cor- rected. Thus, the nee- dle N S, Fig. 32, points to 31 degrees on the scale. In reality, if the magnetic axis of the needle lies in the line N' S', the true deflec- tion of the needle is only 28 degrees.

Fig-. 33. Magnet! Axis.

Axis of Abscissas. — (See Abscissas, Axis of?)

Axis of Ordinates.— (See Ordinates, Axis of?)

Azimuth. — In astronomy, the angular dis- tance between an azimuth circle and the meridian.

The azimuth of a heavenly body in the North- ern Hemisphere is measured on the arc of the horizon intercepted between the north point of the horizon and the point where the great circle that passes through the heavenly body cuts the horizon.

Azimuth Circle.— (See Circle, Azimuth?)

Azimuth Compass. — (See Compass, Azi- muth?)

Azimuth, Magnetic The arc inter- cepted on the horizon between the magnetic meridian and a great circle passing through the observed body.

B. — A contraction used in mathematical writings for the internal magnetization, or the magnetic induction, or the number of lines of force per square centimetre in the magnetized material.

This contraction for internal magnetization is,

in most mathematical treatises, printed in bold- faced type.

B. A. Ohm.— (See Ohm, B. A?)

B. A. U. — A contraction sometimes em- ployed for the British Association unit or ohm.

B. W. G.]

[Bal.

B. W. G.— A contraction for Birmingham wire gauge. (See Gauge, Birmingham Wire.)

A contraction sometimes used for the new British wire gauge.

Back Electromotive Force.— (See Force, Electromotive, Back?)

Back-Stroke of Lightning.— (See Light- ning, Back- Stroke of.)

Bain's Chemical Recorder.— (See Re- •corder, Chemical, Bain's.)

Bain's Printing Solution.— (See Solution, Bain's Printing.)

Balance Arms. — (See Arms, Bridge or Balanced)

Balance, Bi-fllar Suspension An

instrument similar in construction to Cou- lomb's torsion balance, but in which the needle is hung by two separate fibres instead of by a single one. (See Balance, Coulomb's Torsion. Suspension, Bi-filar.)

Balance, Centi-AmpSre An arr-

meter in the form of a balance, whose scale is graduated to give direct readings in centi- amperes.

Ampere balances giving readings in various decimals or multiples of amperes have been de- vised by Sir William Thomson. The strength of current passing is determined by the action on a movable ring or coil, placed between two fixed rings or coils.

The movable ring is in a horizontal plane nearly midway between the two fixed rings. The fixed rings are traversed by the current in opposite directions, so that one attracts and the other repels the movable ring. The movable ring is attached to one end of a horizon- tal balance arm, and a similar movable ring, also provided with attracting and repelling fixed rings, is attached to the opposite end of the balance arm. In order to avoid disturbance of horizontal com- ponents of terrestrial, or of local magnetic force, the current is sent in the same direction through the two movable rings. The balancing is effected by means of a weight, sliding on a nearly hori- zontal arm attached to the balance. A counter- poi^e weight is used in connection with the sliding weight.

A standard Thomson centi-ampere balance is shown in Fig. 33. In measuring a current,

F'S- 33- Centi-Amplre Balance. the weight is moved along the scale until the balance comes to rest.

Balance, Composite — A balance

form of ammeter devised by Sir William Thom- son, which can be used for an ampere-meter, a watt-meter, or a volt-meter, according to the manner in which its sets of fine and coarse wire coils are connected. (See Balance, Centi- Ampere.)

Balance, Coulomb's Torsion An

apparatus to measure the force of electric or magnetic repulsion between two similarly charged bodies, or between two similar mag- net poles, by opposing to such force the tor- sion of a thin wire.

The two forces balance each other ; hence the origin of the name.

Fig. 34. Coulomb's Torsion Balance.

Fig. 34 represents a Coulomb torsion bal- ance, adapted to the measurement of the force

Bal.]

39

[Bal.

of electrostatic repulsion. A delicate needle of shellac, having a small gilded pith ball at one of its ends, is suspended by a fine metallic wire. A proof -plane, B, is touched to the electrified surface whose charge is to be measured, and is then placed as shown in the figure. (See Plane, Proof.) There is a momentary attraction of the needle, anvx t..^~« a repulsion, which causes the needle to be moved a ^.'^in distance from the ball on the proof-plane. This distance is measured in degrees on a graduated circle a a, marked on the instru- ment. The force of the repulsion is calculated by determining the amount of torsion required to move the needle a certain distance toward the ball of the electrified proof-plane.

This torsion is obtained by the movement of the torsion head D, the amount of which motion is measured on a graduated circle at D. The measurement is based on the fact that the force re- quired to twist a wire is proportional to the angle of torsion.

Balance, Deci-Ampere An ammeter

in the form of a balance, whose scale is graduated to give direct readings in deci- amperes. (See Balance, Centi-Ampere^)

Balance, Deka-Ampere — An am- meter in the form of a balance, whose scale is graduated to give direct readings in deka- amperes. (See Balance, Centi-Ampere^)

Balance, Electric A term fre- quently used for Wheatstone's electric bridge. (See Bridge, Electric!)

The electric bridge is sometimes called a balance because, when in use in measuring resistances, one resistance or set of resistances balances an- other resistance or set of resistances.

Balance, Hekto-Ampdre An am- meter in the form of a balance, whose scale is graduated to give direct readings in hekto- amperes. (See Balance, Centt'-Ampere.)

Balance Indicator.— (See Indicator, Bal- ance.)

Balance, Induction, Hughes'

An apparatus for the detection of the presence of a metallic or conducting substance by the aid of induced electric currents.

Hughes' induction balance is shown in Fig. 35.

A, B, C and D are bobbins, wound with about 300 feet of No. 32 copper wire. The coils are

connected as shown, A and B, in the circuit of a battery, and C and D, in the circuit of a telephone. The coils, A and B, and C and D, are placed at

Fig 33. Hughes' Induction Balance.

such a distance apart as to prevent any mutual induction occurring between them. The coils are so joined that the direction of the induction of A, on C, is opposite to that of B, on D.

The coils, A and B, then act as primaries, and C and D, as secondaries. In the battery circuit is an interrupter I, which is caused to continually make and break the circuit.

The coils are so adjusted that the opposing secondary coils produce but little noise to one listening at the telephone. This can readily be done by the adjusting of a single pair of coils.

If a single coin or mass of metal be introduced between either A and C, or B and D, or even above one of the coils, as at d, the balance will be disturbed, since some of the induction is now expended in producing electric currents in the interposed metal, and a sound will therefore be heard in the telephone. But if precisely similar metals are placed in similar positions, between A and C, and B and D, no sound is heard in the telephone, since the inductive effects due to the two metals are the same.

The slightest difference, however, either in composition, size or position, destroys the balance, and causes a sound to be heard in the telephone.

A spurious coin is thus readily detected when compared with a genuine coin.

A somewhat similar instrument has been em- ployed to detect and locate a bullet or other for- eign metallic substance in the human body.

In order to determine the amount of the dis- turbance, an instrument called a sonometer is . used (See Sonometer, Hughes'), in which a single secondary coil, placed in the circuit of a telephone, slides on a graduated bar between two fixed primary coils, so wound as to exert equal and op- posite inductions on the secondary. When, there- fore, the secondary is exactly in the middle of the

Bal.]

40

[Bal.

graduated bar, and consequendy exactly midway between the two fixed primary coils, no sounds are heard in the telephone, but when moved to one side or the other the sounds are heard. Switches are so arranged that the telephone can be readily switched from the induction balance to the tele- phone, or vice versa. When, therefore, a metallic disc is> placed in one of the coils of the induction balance, and a noise is heard in the telephone, the coil of the sonometer is shifted so that the noise heard in this telephone is judged by the ear to be equal, and the comparison can then be made by means of simple calculations.

The following table gives, in arbitrary values, the results of various experiments as to the sensi- tiveness in this respect of discs of different metals, of various sizes and shapes :

Silver, chemically pure 125

Gold 117

Silver, commercial 115

Aluminium 112

Copper too

Zinc 80

Bronze 75

Tin 74

Iron, ordinary 53

German silver 5°

Iron, pure 40

Copper, alloyed 40

Lead ; 58

Antimony 35

Bismuth IO

Zinc, alloyed 6

Carbon 2

; —(Fleming.)

An inspection of this table shows that the values found for different metals do not correspond with their electric conducting power, although, roughly speaking, the best conductors stand at the top of the table, and the worst at the bottom. The effects appear to be dependent for their action on the phenomena of magnetic screening, for —

(i.) If slots are cut in the middle of the plate its disturbing action is either removed or very much decreased.

(2.) If a flat coil of copper wire replaces a disc of metal no effect is produced on the induction balance when its ends are open, bui when closed the coil acts just like a disc, or continuous plate of metal.

(3.) The difference between various metals in-

serted as discs in the induction balance is less at high speeds of reversal than at low speeds.

Balance, Kilo-Ampere — An am- meter in the form of a balance, whose scale is graduated to give direct readings in kilo-am- peres. (See Balance, Centi- Ampere.}

Balance of Induction in Cable. _o Induction, Balance of, in Cab! . J

Balance, Plating — — An automatic device for disconnecting the current from the article to be plated, as soon as a certain increase in weight has been obtained.

The objects to be plated are suspended at one end of a balance, and when a certain increase in weight has been gained, the balance tips and breaks the circuit Edison's electric meter is based on this principle.

Balance, Thermic, or Bolometer. — An

apparatus constructed on the principle of the differential galvanometer, devised by Professor Langley for determining small differences of temperature. (See Galvanometer, Differen- tial)

A coil composed of two separately insulated wires, wound together, is suspended in a mag- netic field, and has a current sent through it. Under normal conditions, this current separates into two equal parts, and runs through the wires in opposite directions. It therefore produces no sensible field, and suffers no deflection by the field in which it is suspended.

Any local application of heat producing a dif- ference in temperature in these coils, causing a difference in resistance, prevents this equality. A field is therefore produced in the suspended coil, which, though extremely small, is rendered meas- urable by means of the powerful field produced in the coil, within which the double coil is sus- pended.

Differences of temperature as small as one- fourteen thousandth of a degree Fahrenheit are detected by the instrument.

Balance, Wheatstone's Electric — —A name often given to the electric bridge or balance. (See Bridge, Electric.}

Balanced-Metallic Circuit.— (See Circuit, Balanced-Metallic)

Balanced Resistances.— (See Resistances, Balanced^

Bal.

41

[Bar.

Balata. — An insulating material. Balata, when prepared for use as an insulating material, is somewhat like gutta-percha.

Ball, Electric Time — — A ball, sup- ported in a prominent position on a tall pole, and caused to fall at the exact hour of noon, or at any other predetermined time, for the purpose of thus giving correct time to an entire neighborhood.

The release of the ball is effected by the closing of an electric circuit, either automatically, or through the agency of an observer.

Ball, Fire A term sometimes ap- plied to globular lightning. (See Lightning, Globular?)

Ball Lightning.— (See Lightning, Ball.} Ballistic Curve.— (See Curve, Ballistic}

Ballistic Galvanometer.— (See Galva- nometer, Ballistic.}

Balloon, Electric A balloon, or

air ship, provided with electric power so as to be able to be steered or moved against the direction of the wind.

Electric balloons have been moved against the wind and steered with a certain amount of success, by the use of electric motors driven by storage batteries. All that is needed to make aerial navi- gation a commercial success is the ability to ob- tain great power with a small weight. The storage battery does this to a limited extent.

Bearing in mind the high efficiency of the elec- tric motor, it would appear that the problem of successful aerial navigation will be solved when the discovery is made of means for directly con- verting the chemical potential energy of coal into electrical energy.

Balloon Signaling for Military Pur- poses.— (See Signaling, Balloon, for Mil- itary Purposes}

Balls, Pith — —Two balls of pith, sus- pended by conducting threads of cotton to insulated conductors, employed to show the electrification of the same by their mutual repulsion.

The pith balls connected with the insulated cylinder A B, Fig. 36, not only show the electri- fication of the cylinder, but serve also to roughly

indicate the peculiarities of distribution of the charge thereon.

Fig. 36. Pith Ball Cylinder.

Bands, Anroral Approximately

parallel streaks of light sometimes seen during the prevalence of the aurora. (See Aurora Borealis^)

Bank of Lamps.— (See Lamps, Bank of} Banked Battery.— (See Battery, Banked}

Bar, Detorsion — —A bar placed in a magnetic instrument called a declinometer for the purpose of removing the torsion of the suspending thread of the magnet.

The detorsion ^ar of the declinometer is gen- erally made of gun metal of the same weight as that of the suspended magnet. A small magnet is placed in a rectangular aperture in the middle of the bar.

Bar Electro-Magnet.— (See Magnet, Electro, Bar}

Barad. — A unit of pressure proposed by the British Association.

One barad equals one dyne per square centi- metre.

Barometer. — An apparatus for measuring the pressure or weight of the atmosphere.

Barometric Column. — (See Column, Baro- metric.)

Bars, Bus Omnibus bars. (See

Bars, Omnibus}

Bars, Krizik's — Cores of various

shapes, provided for solenoids, in which the distribution of the metal in the bar is so pro- portioned as to insure as nearly as possible a uniform attraction or pull while in different positions in the solenoid.

Ban]

42

[Bat.

Krizik's bars of various shapes are shown in Fig. 37. It will be observed that in all cases the

Fig. 37. Krizik's Bars.

mass of metal is greater toward the middle of the core than near the ends.

When a core of uniform diameter is drawn into a solenoid, the attraction or pull is not uniform in strength for different positions of the bar. When the bar is just entering the solenoid, the pull is strongest ; as soon as the end passes the middle of the core the attraction decreases, until, when the centres of the bar and core coincide, the motion ceases, since both ends of the solenoid attract equally in opposite directions. By proportioning the bars, as shown in the figure, a fairly uniform pull for a considerable length may be obtained.

Bars, Negative-Omnibus — The

bus-bars that are connected with the negative terminal of the dynamos. (See Bars, Omni- bus)

Bars, Neutral-Omnibus The bus- bars that are connected with the neutral dynamo terminal in a three-wire system of distribution.

Bars, Omnibus Heavy bars of con- ducting material connected directly to the poles of dynamo-electric machines, in electric incandescent light or electric railway installa- tions, and therefore receiving the entire current produced by the machine.

Main conductors common to two or more dynamos in an electrical generating plant.

The terms bus and omnibus bars refer to the fact that the entire or whole current is carried by them.

Bars, Positive-Omnibus — —The bus- bars that are connected with the positive terminal of the dynamos.

Bath, Bi-polar — — An electro-thera- peutic bath, the current applied to which enters at one part of the tub, and leaves at another part.

The electrodes for the bi-polar bath consist of suitably shaped copper plates, generally called shovel electrodes.

Bath, Copper— —An electrolytic bath containing a readily electrolyzable solution of a copper salt, and a copper plate acting as the anode, and placed in the liquid near the object to be electro-plated, which forms the kathode. .(See Plating, Electro)

The sulphate, the cyanide and the acetate of cop- per are used for copper baths. The use of the sul- phate is objectionable. The cyanide is expensive. The acetate is therefore very generally employed. Wahl gives the following formula for a copper bath, viz. :

Water i ,000 parts.

Acetate of copper, crystal- lized 20 "

Carbonate of soda 20 "

Bisulphite of soda 20 "

Cyanide of potassium (pure) 20 "

Bath, Electro-Plating — —Tanks con- taining metallic solutions in which articles are placed so as to be electro-plated. (See Plating, Electro)

Strictly speaking a plating bath includes not only the vessel and its metallic solution, but also the metallic plate acting as the anode and the article to be plated forming the kathode.

Bath, Electro-Therapeutic — — A bath furnished with suitable electrodes and used in the application of electricity to curative purposes.

Such baths should be used only under the advice of a regular physician.

Bath, Gold — An electrolytic bath

containing a readily electrolyzable solution of a gold salt and a gold plate acting as the anode, and placed in the liquid opposite the object to be plated, which forms the kathode. (See Plating, Electro)

Electro gilding may be accomp'islied either with or without the aid of heat. Hot gilding appears to give a smoother and cleaner deposit.

The following is a fairly good solution for a gold bath:

Water 1,000 parts.

Cyanide of potassium, pure. . 20 "

Gold 10 "

— (Wahl.)

Bat.]

43

[Bat.

The gold is first converted into neutral chloride by dissolving it in 25 parts of pure hydrochloric acid to which 12.5 parts of pure nitric acid has been added. When the gold is completely dis- solved, the liquid is heated until of a dark red color, in order to expel any excess of acid.

Bath, Head, Electric A variety

of electric breeze, applied therapeutically to the head of the patient.

The patient is placed on an insulating stool and connected with one pole of an electrostatic induc- tion machine, the other pole of which is con- nected to a circle of insulated points suspended over the head.

Bath, Hydro-Electric A bath in

which electro-therapeutic treatment is given by applying one electrode to the metallic lining of the tub, and the other electrode to the body of the bather.

Bath, Multipolar-Electric An

electro-therapeutic bath, in which more than two electrodes are employed.

It is not clear that the multipolar-electric bath possesses any decided advantages over the bi-polar bath.

Bath, Nickel An electrolytic bath

containing a readily electrolyzable salt of nickel, a plate of nickel acting as the anode of a battery and placed in the liquid near the object to be coated, which forms the kathode. (See Plating, Electro)

The double sulphate of nickel and ammonium (from 5 to 8 parts dissolved in 100 parts of water) is used for the bath. Some prefer to add sulphate of ammonium and citric acid to the above solution.

Bath, Shower, Electric A shower

bath in which the falling drops carry 'electric charges to the patient subjected thereto.

The water is rendered slightly alkaline. One pole is immersed in the alkaline water and the other connected to a metallic stool on which the patient is placed.

Bath, Silver An electrolytic bath

containing a readily electrolyzable salt of silver and a plate of silver acting as the anode of an electric source and placed in the liquid near the object to be coated, which forms the kathode. ^See ^lating, Electro?)

The double cyanide of silver and potassium is the salt usually employed in the silver bath.

The following bath is recommended by Rose- leur:

Water 1,000 parts.

Cyanide of potassium (pure) 50 " Pure silver 25 "

The silver (granulated) is treated with pure nitric acid (43 degrees Beaum€) and converted into nitrate of silver. The solution is then heated to drynessand subsequently fused. The fused nitrate so obtained is dissolved in fifteen times its weight of distilled water and treated with a solution of cyanide of potassium (10 per cent, of the cyanide), by means of which silver cyanide is thrown down as a precipitate. This precipitate is then sepa- rated and washed. It is added to the 1,000 parts of water, dissolved, and the cyanide of potassium afterward added, thus forming the double cyan- ide required for the bath.

Bath, Stripping — — A bath for remov- ing an electro-plating of gold, silver, or other metal, either by simple dipping or by electric action.

Bath, Ungilding — — A stripping bath suitable for the removal of a coating of gold. (See Bath, Stripping)

Bath, Unipolar-Electric An electro- therapeutic bath, the water of which forms one of the electrodes of the source, and the other electrode is attached to a metallic rod fixed at a convenient height above the tub.

The bath tub is formed of non-conducting sub- stances. The terminals of the electrode con- nected with the water terminate in metal plates located at suitable points in the tub. The cur- rent is applied by the patient making and break- ing contact at the vertical metal rod with his hands.

The unipolar-electric bath is employed instead of local galvanization where it is desired to limit the application to especial organs or particular parts of the body. In general galvanization the patient is placed on an electrode of large sur- face, formed of a large spxjnge- covered metallic plate, on which he sits or rests. This electrode is connected with the kathode of the battery. The anode is connected with a large sponge electrode, which is moved regularly over the body of the patient; sometimes the moistened hand of the operator is used in place of the sponge electrode.

Bat.]

[Bat.

Bath, UnsilTering — — A stripping bath suitable for the removal of a coating of silver. (See Bath, Stripping^

Bathometer. — An instrument invented by Siemens for obtaining deep-sea soundings without the use of a sounding line.

The bathometer depends for its operation on the varied attraction of the earth for a suspended weight in parts of the ocean differing in depth. As the vessel passes over deep portions of the ocean, the solid land of the bottom, being further from the ship, exerts a smaller attraction than it would in shallow parts, where it is nearer; for, although in the deep parts of the ocean the water lies between the ship and the bottom, the smaller density of the water as compared with the land causes it to exert a smaller attraction than in the shallower parts, where the bottom is nearer the ship. The varying attraction of the earth is caused to act on a mercury column, the reading of which is effected by means of an electric con- tact.

Battery, Banked — A term some- times applied to a battery from which a num- ber of separate circuits are supplied with cur- rents.

The term banked-battery is sometimes ap- plied to a multiple-arc connected battery.

Battery, Cautery — —A term some- times employed in electro-therapeutics, for a multiple connected voltaic battery adapted for producing electric incandescence for cautery effects.

Battery, Closed-Circuit - —A voltaic battery which may be kept constantly on closed-circuit without serious polarization.

The gravity battery is a closed -circuit battery. As employed for use on most telegraph lines, it is maintained on a closed circuit. When an operator wishes to use the line he opens his switch, thus breaking the circuit and calling his correspondent. Such batteries should not polarize. (See Cell, Voltaic, Polarization of.)

Battery, Connection of, for Quantity —

— A term, now generally in disuse, formerly employed to indicate the grouping of voltaic cells, now known as parallel or multiple.

The arrangement or coupling of a number of voltaic cells in multiple reduces the internal resist-

ance of the battery, and thus permits a greater current, or quantity, of electricity to pass ; hence the origin of the term.

Battery, Dynamo The combina- tion or coupling together of several separate dynamo-electric machines so as to act as a single electric source.

The dynamos may be connected to the leads either in series, in multiple, in multiple-series or in series-multiple.

Battery, Dynamo, Electric Machine —

— A dynamo battery. (See Battery, Dy- namo?)

Battery, Electric A general term

applied to the combination, as a single source, of a number of separate electric sources.

The separate sources may be coupled either in series, in multiple, in multiple-series, or in series- multiple. ( See Circuits, Varieties of.)

The term battery is sometimes incorrectly ap- plied to a single voltaic couple or cell.

Battery, Floating, De la Rive's — —A

floating voltaic cell, the terminals of which are connected with a coil of insulated wire, em- ployed to show the attractions and repul- sions between magnets and movable electric circuits.

The cell, shown in Fig. 38, consists of a vol-

Fig. 38. Floating Cell.

taic couple of zinc and copper, the terminals of which are connected to the circular coil of insu- lated wire, as shown, and the whole floated by means of a cork, in a vessel containing dilute sul- phuric acid.

When the current flows through the coil in the direction shown by the arrows, the approach of the N-seeking pole of a magnet will cause the cell to be attracted or to move towards the mag- net pole, since the south face or end of the coil is nearer the north pole of the magnet. If the other

Bat.]

[Bat.

end were nearer, repulsion would occur, the cell turning round until the south face is nearer the magnet, when attraction occurs.

This is, strictly speaking, a floating cell, and not a battery. (See Battery, Voltaic.}

Battery, Galvanic Two or more

separate voltaic cells so arranged as to form a single source.

This is more correctly called a Voltaic Battery. (See Battery, Voltaic.)

Battery, Gas A battery in which

the voltaic elements are gases as distinguished from solids.

The electrodes of a gas battery generally con- sist of plates of platinum, or other solid substance which possesses the power of occluding oxygen and hydrogen. The lower parts of these plates dip into dilute sulphuric acid, and the upper parts are respectively surrounded by oxygen and hydro- gen gas derived from the electrolytic decompo- sition of the dilute acid.

A gas battery consisting of plates of platinum dipping below into acid liquid, and surrounded in the space above the liquid by hydrogen and oxygen H, H' and O, O', etc., respectively is shown in Fig. 39.

Fig- 39- Gas Battery.

In charging this battery an electric current is sent through it until a certain quantity of the gases has been produced. If, then, the charging current be discontinued, a current in the oppo- site direction is produced by the battery. The gas battery is in reality a variety of storage bat- tery. (See Electricity, Storage of. Cell, Secon- dary. Cell, Storage.")

Gas batteries can also be made by feeding con- tinually into the cell a gas capable of acting on the positive elements.

Battery Gauge. — (See Gaugi, Battery?)

Battery, Leyden Jar The combina- tion of a number of separate Leyden jars so as to act as one single jar.

A Leyden jar battery is shown in Fig. 40,

Fig. 40, Leyden Jar Battery.

where nine separate Leyden jars are connected as a single jar by joining their outer coatings by placing them in the box P, the bottom of which is lined with tin foil. The inner coatings are connected together by the metal rods B, as shown.

A discharging rod A, may be employed for connecting the opposite coatings. The handles are made of glass or any other good insulating material.

A number of Leyden jars can be coupled in series by connecting the inner coating of the first jar to the outer coating of the second, the inner coating of the second to the outer coating of the third, and so on. The battery so obtained is then discharged by connecting the outer coat, ing of the first jar with the inner coating of the last.

Battery, Local A voltaic battery

used at a station on a telegraph line to operate the Morse sounder, or the register- ing or recording apparatus, at that point only. (See Telegraphy, American or Morse System of.)

The local battery is thrown into or out of action by the telegraphic relay. (See Relay.}

Battery, Magnetic -The combina- tion, as a single magnet, of a number of sep- arate magnets.

A magnetic battery, or compound magnet, is

Bat.]

[Bat.

Fig, J.T, Magneti Battery, or Com

shown in Fig. 41. It consists of straight bars of steel, p, p, p, with their similar poles placed near together and inserted in masses of soft iron, N and S, as shown.

Battery, Main

The battery, in a system of telegraphic communi- cation, that is employed for sending the signals over the main line, as dis- tinguished from any bat- tery employed for any other particular work, such, for example, as that of the local battery. (See Battery, Local.)

Battery, Multiple-Con- found Magnet.

nected A battery the single cells of

which are connected to one another and to the mains or conductors in multiple. (See Cir- cuit, Multiple)

Battery, Open-Circuit A voltaic

battery which is normally on open-circuit, and which is used continuously only for com- paratively small durations of time on closed- circuit.

Leclanche'-cells form an excellent open-circuited battery. 'They have a comparatively high electro- motive force, but rapidly polarize. They cannot therefore be economically used for furnishing currents continuously for long durations of time. When left on open-circuit, however, they readily depolarize. They therefore form an excellent battery for such work as annunciator bells, burg- lar alarms, etc., where the current is only required for short periods of time, separated by comparatively long intervals of rest. (See Cell, Voltaic, Leclanche.)

Battery Plates of Secondary or Storage

Cell, Forming of (See Plates of

Secondary or Storage Cell, Forming of.)

Battery, Plunge A number of

separate voltaic cells connected so as to form a single cell or electric source, the plates of which are so supported on a horizontal bar as to be capable of being simultaneously placed in, or removed from, the exciting liquid.

The plunge battery shown in Fig. 42, consists

Fig. 42. Plunge Battery,

of a number of zinc-carbon elements immersed in an electrolyte of dilute sulphuric acid, or in elec- tropoion liquid, contained in separate jars, J, J. (See Liquid, Electropoion.)

The mode of support to the horizontal bar will be understood from an inspection of the drawing.

Battery, Primary The combina- tion of a number of separate primary cells so as to form a single source.

The term primary battery is used in order to distinguish it from secondary or storage battery. (See Cell, Secondary. Cell, Storage.)

Battery, Secondary The combina- tion of a number of separate secondary or storage cells, so as to form a single electric source. (See Electricity, Storage of.)

Battery, Selenium The combina- tion of a number of separate selenium cells so as to form an electric source. (See Cell, Selenium.)

Battery, Series-Connected A bat- tery, the separate cells of which are con- nected to one another and to the line or conductor in series. (See Circuit, Series.)

Battery Solution.— (See Solution, Bat- tery)

Battery, Split A voltaic batten'

connected in series, but having one of its middle plates connected with the ground.

By the employment of the device of a split- battery, the poles of the battery are maintained at potentials differing in opposite directions from the potential of ihe earth.

Battery, Storage — —A number of separate storage cells connected so as to form a single electric source.

Bat.]

[Bel.

A cell of a storage battery is shown in Fig.

43-

Fig. 43. Storage Battery.

Battery, ' Storage, Element of A

single set of positive and negative plates of a storage cell connected so as to be ready for placing in the acid liquid of the jar or cell.

A term sometimes applied to one of the storage cells in a storage battery.

This latter use of the term element is unfortu- nate, since from the analogous case of a primary •cell, an element would consist of a single plate, either positive or negative, and not of both. That is, every voltaic couple consists of two elements, the positive and the negative.

Battery, Thermo A term often

applied to a thermo-electric battery. (See Battery, Thermo- Electric)

Battery, Thermo-Electric The

combination, as a single thermo-electric cell, of a number of separate thermo-electric cells or couples. (See Couple, Thermo-Electric)

Battery, Voltaic The combina- tion, as a single source, of a number of sepa- rate voltaic cells.

Battery, Water A battery formed

of zinc and copper couples immersed in an electrolyte of ordinary water.

Any voltaic couple can be used, the positive element of which is slightly acted on by water. When numerous couples are employed consider- able difference of potential can be obtained.

Water batteries are employed for charging electrometers. They are not capable of giving any considerable current, owing to their great in- ternal resistance.

Bead Areometer or Hydrometer. — (See Areometer, Bead.)

Bec-Carcel. — The Carcel. or French unit of light. (See Carcel)

Bell, Automatic-Electric An elec- tric bell furnished with an automatic contact- breaker. (See Contact-Breaker, Automatic)

A form of automatic-electric bell is shown m Fig. 44. The relation of the electro- magnet, its armature and the bell lever, will be readily understood from an in- spection of the draw- ing.

Bell, Call

An electric bell used to call the attention of an operator to the fact that his corre- spondent wishes to communicate with him.

Bell, Circular

— A bell so construct- ed that all its moving

parts are contained in Figt 44, Automatic EUctrii the gong. Bell.

Bell, Continuous-Sounding Electric —

— An electric bell, which, on the completion of the circuit, continues striking until stopped either by hand or automatically.

On the completion of the circuit, the attraction of an armature throws a catch off from a lever, and thus permits the lever to fall and complete a contact and allows the current to ring the bell; or the bell is rung by clockwork, which is thrown into action by the passage of a current through an electro-magnet. (See Bell, Electro-Mechanical.}

Bell, Differential Electric An

electric bell, the magnetizing coils of which are differentially wound.'

Differential winding is ot advantage where a very strong current is required, as this winding decreases the sparking at the contacts, on the opening of the circuit.

Bell, Electro-Magnetic, Siemens-Arma- ture Form A form of electro-mag-

Bel.]

48

[Bel.

netic bell in which the movements of the bell armature are obtained by the reversal of polarity that takes place when alternating cur- rents are pass- ed through the coils of a sim- ple, single coil, Siemens - arma-

ture> Fig. 4$. Siemens-Armature Form

The details of Electro-Magnetic Bell.

will be readily understood from an examination of Fig. 45.

Bell, Electro-Mechanical A bell,

the striking apparatus of which is driven by a weight or spring, called into action by the movement of the armature of an electro- magnet. (See Alarm, Electric?)

Bell, Extension-Call A device for

prolonging the sound of a magneto call.

An alarm bell is automatically connected with

Fig. 46. Extension-Call Bell.

the circuit of a local battery by means of the cur- rent generated by the magneto-call, and continues sounding after the current of the magneto call has ceased.

A form of extension-call bell is shown in Fig. 46.

Bell, Indicating- An electric bell

in which, in order to distinguish between different bells in the same office, a number is displayed by each bell when it rings.

Bell, Magneto-Electric An electric

bell, the curre.it employed to operate or strike which is obtained by the motion of a magneto-electric machine.

Bell, Night In a telephone ex- change, a bell, switched into connection with the shunted circuit of an annunciator case, and intended, by its constant ringing, to call the attention of the night operator to the falling of a drop.

Bell, Belay, Electric --- An electric bell in which a relay magnet is employed to switch a local battery into the circuit of the sounding apparatus of the bell.

The relay bell is suitable for use when the bell to be sounded is situated at a great distance. As the current from the 1 ine, when this is long, is too weak to ring the bell, it throws into action a local battery by the action of a relay.

Relay bells were used in the early forms oi acoustic telegraphs as employed in England with relay sounders.

The dots and dashes of the Morse alphabet were indicated by the sounds of two bells, a tap on one bell indicating a dot, and a tap on the other a dash. This system is now practically aban- doned.

Bell-Shaped Magnet.— (See Magnet, Sell-

Bell, Shunt, Electric -- An electric bell, the magnetizing coils of which are placed on the line in shunt.

In the case of shunt-connected electric bells, one of the bells must make and break the circuit for all the rest. The series-connected electric bell is used where the distance between the sepa- rate bells is great, in order to save the expense of multiple connections.

In most cases, where a number of electric bells are to be simultaneously sounded, connection in multiple is adopted.

Bell, Single-Stroke Electric --- An

electric bell that gives a single stroke only for each make of the circuit.

Kg. 47. Single-Stroke Bell.

Since the bell gives a single stroke for each completion of the circuit, its use permits of ready communication between any two places by any

Bel.]

40

[Bla.

system of prearranged signals. A buzzer may be used for the same purpose. A form of single- stroke bell is shown in Fig . 47 . On completing the circuit, the current, through its coils, attracts the armature and causes a single stroke of the bell.

Bell, Telephone-Call - —A call bell used to call a correspondent to the telephone.

The telephone-call bell is generally a magneto- electric bell.

Bell, Trembling A name some- times given to a vibrating or an automatic make-and-break bell. (^ezMake-and-Break, Automatic •)

Bell, Yibrating — — A trembling bell. (See Bell, Trembling)

Bias of Relay Tongue. — (See Tongue, Relay, Bias of.}

Bichromate Toltaic Cell.— (See Cell, Vol- taic, Bichromate.)

Bi-fllar Suspension. — (See Suspension, Bi-filar.}

Bi-fllar Suspension Balance.— (See Bal- ance, Bi-filar Suspension)

Bi-fllar Winding.— (See Winding, Bi- filar)

Binary Compound.— (See Compound, Bi- nary)

Binding Coils.— (See Coils, Binding)

Binding-Post— (See Post, Binding)

Binding-Screw.— (See Screw, Binding)

Binding Wire for Telegraph Lines.— (See Wire, Binding, for Telegraph Lines)

Biology, Electro That branch of

electric science which treats of the electric conditions of living animals and plants, and the effects of electricity upon them.

Electro-Biology includes :

(I.) Electro-Physiology.

(2.) Electro-Therapy, or Electro-Therapeutics.

Bioplasm.— Any form of living matter pos- sessing the power of reproduction.

Bioscopy, Electric The determina- tion of the presence of life or death by the passage of electricity through the nerves and muscles.

Bi-polar. — Having two poles.

Bi-polar Armature. — (See Armature, Bi-polar)

Bi-polar Bath.— (See Bath, Bi-polar)

Birmingham Wire Gauge.— (See Gauge, Wire, Birmingham)

Bi-Telephone.— (See Telephone, Bi)

Bitite. — A variety of insulating material.

Black Electro-Metallurgical Deposit— (See Deposit, Black Electro-Metallurgical)

Black Lead. — A variety of carbon em- ployed in various electrical processes.

Black lead is also termed plumbago or graphite. (See Plumbago. Graphite)

The term black lead is a misnomer, since the substance is carbon and not lead. The term is an old one, and is still very generally used.

Blasting, Electric — —The electric ignition of powder or other explosive material in a blast. (See Fuse, Electric)

The current required for the ignition of the fuse is generally obtained by means of a magneto- electric machine. In the form of magneto-blast- ing machine, shown in Fig. 48, the movement

Fig. 48. Magneto-Blasting Machine.

of the handle shown at the top of the figure causes the rapid rotation of a cylindrical armature constructed on the Wheatstone and Siemens prin- ciple. The magnets are of iron, and are furnished

Ble.J

50

[Boa.

with coils of insulated wire. On the rotation of the armature the current developed therein in- creases the field of the field magnet, and, when of the proper degree of intensity, is thrown into the outer circuit, and ignites the fuse.

Bleaching, Electric Bleaching pro- cesses in which the bleaching agents are liberated, as required, by the agency of electro- lytic decomposition.

In the process of Naudin and Bidet, the cur- rent from a dynamo-electric machine is passed through a solution of common salt between two closely approached electrodes. The chlorine and sodium thus liberated react on each other and form sodium hypochloride, which is drawn off by means of a pump and used for bleaching. (See Electrolysis.)

Block, Branch A device em- ployed in electric wiring for taking off a branch from a main circuit. (See Wiring.)

A form of branch-block, with its fuses attached, is shown in Fig. 49.

Fig. 49. Branch-Black.

Block, Cross-Over A device to

permit the safe crossing of one wire over another in molding or cleat wiring.

Block, Fuse A block containing

a safety fuse or fuses for incandescent light circuits. (See fuse, Safety.)

Block System for Railroads.— (See Rail- roads, Block System for.)

Block Wire.— (See Wire, Block)

Blow-Pipe Electric— —A blow-pipe in which the air-blast is obtained by a stream of air particles produced at the point of a

charged conductor by a convection dis- charge. The candle flame, Fig. 50, is blown in the di-

P

Fig. 50. Convection Blow-Pipe.

rection of the stream of air particles passing off from the point P. (See Convection, Electric.)

Blow-Pipe, Electric-Arc A de- vice of Werdermann for cutting rocks, or other refractory substances, in which the heat of the voltaic arc is directed* by means of a magnet, or a blast of air, against the substance to be cut.

The cartons are placed parallel, so as to readily enter the cavity thus cut or fused. This inven- tion has never been introduced into extensive practice.

In the welding process of Benardos and Olzewski, the welding temperature is obtained by means of an electric arc taken between two suit- ably shaped electrodes.

In t!ie electric-arc blow - pipe, shown in Fig. 51, the voltaic arc, taken between two ver- tical carbon electrodes, is deflected into a hori- zontal position under the influence of the inclined poles of a powerful elec- tro-magnet.

The highly heated car- bon vapor which consti- tutes the voltaic arc is deflected by the magnet in the same direction as would be any other mov- able circuit or current.

Board, Cross-Connecting' In a

system of telegraphic or telephonic communi- cation, a board to which the line terminals are run before entering the switchboard, so as to

Fig. 5f. Electric- Arc Blmv-Pipe.

Boa.]

51

[Boa.

readily place any subscriber in connection with any desired section of the switchboard.

Board, Fuse A board of slate or

other incombustible material on which all the safety fuses in an installation are as- sembled.

The fuse board is used for avoiding accidents from the firing of the fuses.

Board, Hanger A form of board

provided for the ready placing or removal of an arc lamp from a circuit.

Fig, <fs* Hanger- Board.

A hanger-board contains a switch or cut-out for the ready opening or closing of the circuit. A form of hanger-board is shown in Fig. 52.

Board, Key Any board to which

are connected electric keys or switches.

Board, Legging-Key A key boaid

employed for the purpose of legging an operator into a circuit connecting two or more subscribers. (See Leg.)

Board, Multiple Switch A board

to which the numerous circuits employed in systems of telegraphy, telephony, annunciator or electric light and power circuits are con- nected.

Various devices are employed for closing these circuits, or for connecting or cross-connecting them with one another, or with neighboring cir- cuits.

A multiple switchboard, for example, for a tele- phone exchange, will enable the operator to con- nect any subscriber on the line with any other subscriber on that line, or on another neighbor-

ing line provided with a multiple switchboard. To this end the following parts are necessary:

(I.) Devices whereby each line entering the ex- change can readily have inserted in its circuit a loop connecting it with another line. This is accomplished by placing on the switchboard a separate spring-jack connection for each sepa- rate line. This connection consists essentially of one or two springs made of any conducting metal, which are maintained in metallic contact when the plug key is not inserted, but which are readily separated from one another by the introduction of the plug- key, Fig. 53, the terminals, a and b, of which are insulated from each other, and are connected to the ends of a loop coming from another line. As the key is in- Fis'53^e Plug' serted, the metallic spring or springs of the spring-jack are separated and the metallic pieces, a and b, are brought into good sliding contact therewith, thus introducing the loop into the circuit. (See Spring- Jack.)

(2.) As many separate annunciator-drops as there are separate subscribers. These are pro* vided so as to notify the Central Office of the par- ticular subscriber who desires a connection. Alarm-bells to call the operator's attention to the calling subscriber, or to the falling of a drop, are generally added. (See Bell, Call.)

(3. ) Connecting cords and keys for connecting the operator's telephone, and means for ringing subscribers' bells, and clearing out drops.

Fig. S4- Multiple Switchboard1 for Electric Light.

In Multiple Switchboards for the Electric Light or Distributing Switches, spring-jack contacts are connected with the terminals of different circuits.

Boa.]

[Bod.

and plug switches with the dynamo terminals. By these means, any dynamo can be connected with any circuit, or a number of circuits can be connected with the same dynamo, or a number of separate dynamos can be placed in the same circuit without interference with the lights.

Board, Switch A board provided

with a switch or switches, by means of which electric circuits connected therewith may be opened, closed, or interchanged.

Board, Switch, Telegraphic A

device employed at a telegraph station by means of which any one of a number of tele- graph instruments, in use at that station, may be placed in or removed from any line con- nected with the station, or by means of which one wire may be connected to another.

The ability to readily connect one wire with another is of use in case of interruption to tele- graph lines, in which case a through circuit may be made up of sections of different circuits.

In the switchboard shown fa Fig. 55, the upper left- hand binding-post is con- nected to earth; the four remaining binding - posts are connected to two sepa- Fig. ss- Telegraphic rate instruments— the sec- Switchboard.

ond and third from the top to one instrument, and the fourth and fifth to another instrument. The four posts at the top of the figure are con- nected to two lines running east and west.

Various connections are made by the insertion of plug keys in the various openings.

Board, Switch, Trnnking —A

switchboard in which a few subscribers only are connected with the operator, thus enabling him to obtain any other subscriber by means of trunk wires extending to the other sections. (See Wire, Trunk)

Boat, Electric —A boat provided

with electric motive power.

Electric power has been applied both to ordi- nary vessels and to submarine torpedo boats.

Boat, Submarine Electric A boat

capable of being propelled and steered while entirely under water.

The motive power of such boats is generally

electricity. The requisite buoyancy is obtained by means of an air chamber. Artificial ventila- tion is maintained, the fresh air requisite for breathing being derived from a compressed air cylinder.

Boat, Torpedo — A boat used for

carrying and discharging torpedoes. (See Torpedo)

Bobbin, Electric An insulated coil

of wire for an electro-magnet.

Body, Charged A body containing

an electric charge.

Charges are bound or free. ' (See Charge, Bound. Charge, Free.}

Body, Electrified —A body con- taining an electric charge. Body, Human, Resistance of •

The resistance which the human body offers to the passage of an electric current.

The resistance of the human body to the passage of a current varies with the time. The re- sistance rapidly decreases after a short time.

"The resistance diminishes because of the con- duction of water in the epidermis under the action of the constant current and the congestion of the cutaneous blood vessels in consequence of the stimulation. ' ' ( Landois and Stirling. )

The resistance also varies markedly with the condition of the surface, the condition of the skin, and with the shape, area, position and material of the electrodes by which the current is led into and carried out of the parts. It very seldom is less than 1,000 ohms under the most favorable conditions, and with ordinary contacts is many times that amount.

The muscles offer nearly nine times the resist- ance in a direction transverse to the fibres than longitudinally to them. (Hermann.)

The resistance of the epidermis is greater than that of any other tissue of the body.

The human body probably possesses a true assymmetrical resistance; that is to say, when taken after the current has been passing for some time, its resistance is different in different direc- tions. This variation in the apparent resistance is believed by some to be due to polarization effects.

Body, Insulated —A body sup- ported on an insulator, or non-conductor of electricity.

Bod.]

[Box.

Body-Protector, Electric . —A de- vice for protecting the human body against the accidental passage of an electric discharge.

To protect the human body from the acciden- tal passage through it of dangerous electric cur- rents, Delany places a light, flexible, conducting wire, A A B L L, in the posi- tion shown in Fig. 56, for the purpose of leading the greater part of the current around instead of through the body. The body-pro- tector thus provides a by- path, or shunt of low resist- ance, around the body, and protects it from the effects of an accidental discharge, f'f- S6. Electric The resistance of the con- Body-Protector. tacts of the protecting conductor with the skin may interfere somewhat with the efficacy of the device. Inside insulating shoe-soles for lessening the danger from accidental contacts through grounded circuits have also been proposed.

Boiler-Feed, Electric —A device

for automatically opening a boiler-feed appar- atus electrically when the water in the boiler falls to a certain predetermined point.

Boiling of Secondary or Storage Cell. — (See Cell, Secondary, or Storage, Boiling of,}

Bole. — A unit, seldom or never used, pro- posed by the British Association.

One bole is equal to one gramme-kine. (See Kine.)

Bolometer.— An apparatus devised by Langley for measuring small differences of temperature.

A thermal balance. (See Balance, Ther- mic)

Bpmbardment, Molecular — The

forcible rectilinear projection from the nega- tive electrode, of the gaseous molecules of the residual atmospheres of exhausted vessels on the passage of electric discharges. (See Matter, Radiant, or Ultra-Gaseous)

Bonsalite. — An insulating substance.

Bore, Armature • —The space pro- vided between the pole pieces of a dynamo or motor for the rotation of the armature.

Boreal Magnetic Pole.— (See Pole, Mag~ netic, Boreal?)

Bot. — A term sometimes used as a con- traction for Board of Trade unit of electric supply, or the energy contained in a current of 1 ,000 amperes flowing in one hour under a pressure of one volt.

The term appears inadmissible. If used at all, it should be B. O. T. The usage of giving the names of distinguished dead electricians to new units is a good one, and should be followed here.

Boucherize. — To subject to the boucheriz- ing process. (See Boucherizing?)

Boucherizing. — A process for the preser- vation of wooden telegraph poles, by inject- ing a solution of copper sulphate into the pores of the wood. (See Pole, Telegraphic?)

Bound Charge.— (See Charge, Bound)

Box Bridge.— (See Bridge, Box)

Box, Cable —A box placed on a

large terminal pole and provided to receive the separate conductors where the air-line wires join a cable.

The wires are distributed in the cable box so as to be readily attached to the air-line wires.

Box, Cooling, of Hydro-Electric Ma- chine. — A box provided in Armstrong's hydro-electric machine for the steam to pass through before leaving the nozzle.

In passing through the cooling-box some of the steam suffers condensation. The cooling-box, therefore, always contains some water, the pres- ence of which seems to be necessary to the opera- tion of the machine.

Box, Distributing, of Conduit. — A name generally applied to a handhole of a conduit. (See Handhole of Conduit)

Box, Distribution, for Arc Light Cir- cuits.— A device by means of which arc and incandescent lights may be simultane- ously employed on the same line from a con- stant-current dynamo-electric machine or other source of constant currents.

A portion of the line circuit, whose difference of potential is sufficient to operate the electro- receptive device, as, for example, an incandescent lamp, is divided into such a number of multiple

Box.]

[Box.

circuits as will provide a current of the requisite strength for each of the devices. For example, if the normal current on the line is seven amperes, then each of the seven multiple-connected electro-

Fig. J7. Series- Multiple Circuit. receptive devices shown in Fig. 57 will have a cur- rent of one ampere passing through it, provided the resistance of each branch is the same,

In order to protect the remaining devices from variations in the current on the extinguishment of any of the devices, automatic cut-outs are pro- vided, which divert the current thus cut off through a resistance equivalent to that of the device.

A variety of distribution boxes are in use. (See Circuits, Varieties of.)

Box, District-Call A box by

means of which an electric signal is auto- matically sent over a telegraphic line and received by an electro-magnetic device at the other end of the line.

motion by the pulling of a lever, makes and breaks an electric circuit and sends over the line a succession of electric impulses of varying length, separated from one another by varying intervals of time. These impulses may be received at the central station as a series of dots and dashes, or may, by means of a Morse sounder, produce suc- cessive sounds. By pulling the lever or handle through different distances, different signals may be sent to the central station and serve as calls for various services, such as messenger boys, fire alarm, police, special, etc.

The general appearance of a four-call district box is shown in Fig. 58. In order to transmit a call for any particular one of these four services the handle is pulled until it comes opposite to the letters indicating the required service, and is then released. The service required is then indicated at the receiving, or central station, through the varying signals sent over the line by the move- ment of the break-wheel, on the release of the handle.

Box, Fire-Alarm Signal — —A signal box provided for the purpose of automatically sending an alarm of fire.

The fire-alarm box shown in Fig. 59, operates

Fig. 38. District Call Box.

A system of district calls includes a number of call boxes connected by telegraphic lines with a central station, A wheel, or its equivalent, set in

Fig. j-p. Fire- Alarm Signal-Box.

on the same principle as the district call box. The movement of the handle in the direction of the arrow drives a wheel that makes and breaks a circuit at certain intervals.

The fire-alarm signal boxes are connected

Box.]

[Box.

either with a central station, or with the engine houses of the district in which the alarm is sounded, or with both.

Box, Fire- Alarm Telegraph An

automatic-call signal-box employed for send- ing an alarm of fire to a central station.

A form of fire-alarm telegraph box is shown in Fig. 60. It consists essentially of a circuit-breaker

Fig. 6O. Fire- Alarm Telegraph Box. that is moved by pulling down a lever. The release of the lever repeats the signal to the fire department at the central station a certain number of times. The box also contains a relay bell, lightning arrester and signal-bell key.

Box, Fishing A term sometimes

used instead of junction box. (See Box, Junction. )

Box, Flush A box or space, flush

with the surface of a road-bed, provided in a system of underground wires or conduits, to facilitate the introduction of the conduct- ors into the conduit, or for the examination of the conductors.

Box, Fuse The box in which the

fuse-wire of a safety-fuse is placed.

The fuse-box should be formed of moisture- proof, Incombustible, insulating materials.

Box, Junction A moisture-proof

box provided in a system of underground con-

the feeders and the mains, and from which the current is distributed to the individual consumer. (See Feeder. Main, Electric^)

A form of junction box for coupling lengths of conductors is shown in Fig. 6l.

Box, Patrol Alarm An automatic- signal call-box provided for use on the out- side of buildings.

The call-box is placed inside a box, the outer door of which is furnished with a Yale lock.

Fig. 6 1. Junction Box.

ductors to receive the terminals of the feed- ers, in which connection is made between

Fig. 62. Patrol Box.

A form of patrol box is shown in Fig. 62.

Box, Resistance A box containing

a number of separate coils of known resist- ances employed for determining the value of an unknown resistance, and for other pur- poses. (See Bridge, Electric, Box Form of.)

Box-Sounding Relay.— (See Relay, Box- Sounding)

Box-Sounding Telegraphic Relay.— (See

Relay, Box-Sounding Telegraphic.)

Box, Splice A box provided for

holding splice joints and loops, and so ar- ranged as to be readily accessible for exami- nation, re-arranging, cross-connecting, etc.

Splice-boxes vary in shape and construction according to the purposes for which they are designed.

Box, Splice, Four-way A splice- box piovided with four ways or tubular con- duits.

Box, Splice, Two Way A splice-

Box.J

[Bra.

box provided with but two tubular conduits or ways.

Box, Tumbling A rotating box

in which metallic articles that are to be electroplated are placed so as to be polished by attrition against one another.

Boxing the Compass. — (See Compass, Boxing the?)

Bracket, Lamp, Electric A de- vice similar to a bracket for a gas burner for holding or supporting an electric lamp.

Fig. 63. Lamp Bracket. Fig. 6 4. Lamp Bracket. Lamp brackets are either fixed or movable.

Fig. 6j. Lamp Bracket, Movable Arms. Those shown in Figs. 63 and 64 are fixed. That shown in Fig. 65 is movable.

Bracket, Telegraphic A support

or cross piece placed on a telegraph pole for the support of the insulators of tele- graphic lines.

Telegraphic insulators are supported either on wooden arms, or on iron or metal brackets.

Fig. 66 shows a form of iron bracket. Fig. 67 shows a form of wooden arm.

Fig. 66. Telegraphic Bracket.

Fig. 67. Telegraphic Cross- Arm.

Various well known modifications of these shapes are in common use. (For details, see Fole, Telegraphic. )

Braid, Tubular A braid of fibrous

insulating material, woven in the form of a tube, and provided for drawing over a splice after two wires have been connected.

Braided Wire.— (See Wire, Braided)

Brake, Electro-Magnetic A brake

for car wheels, the braking power for which is either -derived entirely from electro-magnet- ism, or is thrown into action by electro-mag- netic devices.

Electro-magnetic car brakes are of a great va- riety of forms. They may, however, be arranged in two classes, viz. :

(l.) Those in which magnetic adhesion, or the magnetic attraction of the brake to the wheels, is employed.

(2.) Ordinary brake mechanism in which the force operating the brake is thrown into action by an electro-magnet.

Brake, Friction A name some- times given to a Prony brake. (See Brake, Prony.)

Brake, Magneto-Electric A device

for checking the swing of a galvanometer, in which a slight inverse current is sent through the coils of the galvanometer.

The Frey magneto-electric brake, as shown in Fig. 68, consists of a small coil, connected by a

Fig. 68. Electric Brakt.

contact-key with the galvanometer terminals. A small adjustable magnet coil is provided for regulating the action ot the inverse current. To avoid disturbance, the brake is placed at least 4 or 5 feet from the galvanometer. Manipulation of the ordinary galvanometer key attains the same end in a much simpler manner.

Brake, Prony A mechanical de- vice for measuring the power of a driving shaft.

Bra.j

57

[Bre.

An inflexible beam, Fig. 69, is provided at one end with a clamping device for clamping the driving shaft or pulley, and at the other end A, with a pan for holding weights.

If the brake be arranged as shown in Fig. 69, and the shaft rotate in the direction of the arrow, the tendency will be to carry the beam around with the shaft, placing it at some given moment

Fig, 69, Pr any Brake.

in the position shown by the dotted line. If a sufficiently heavy weight be placed at x, in a pan hung at A, the beam will assume a position ver- tically downwards. If, however, the torque, or

Fig. 70. Prony

twisting force of the driving shaft, be balanced by the weight, the bar will remain horizontal. The power can then be calculated by multiplying the weight in pounds by the circumference in feet of the circle of which the bar is a radius, and this product by the number of turns of the driving shaft per minute. The product will be the num-

» V

Fig. 7 TC Prony Brake.

ber of foot-pounds per minute, and, when divided by 33,000, will give the horse-power.

Some modified forms of the Prony brake are shown in Figs. 7° and 71.

A simple form of brake consists of a cord passed over the pulley of the machine to be tested. A weight is hung at one end of the cord. The other

end of the cord is attached to the top of a spring balance, the other end of which is fastened to the floor. A reading of the spring balance is taken while the pulley is at rest and when it is in motion, and the result calculated.

Branch. — A term applied to any principal distributing conductor from which outlets are taken or taps made.

Branch-Block.— (See Block, Branch)

Branch Conductors. — (See Conductor, Branch)

Branch Fuse.— (See Fuse, Branch.}

Branch, Sub —A distributing con- ductor taken from a branch.

Branding, Electric - - — A process whereby the branding tool is heated by elec- trical incandescence instead of by ordinary heat.

The branding tool consists essentially of a small transformer with devices for regulating the cur- rent strength by switches and choking coils.

Brassing, Electro — Coating a sur- face with a layer of brass by electro-plating. (See Plating, Electro)

The plating bath contains a solution of copper and zinc ; a brass plate is used as an anode.

Break. — A want of continuity in a circuit.

Break, Circuit Loop — — A device for introducing a loop in any part of a line circuit.

A form of circuit loop-break is shown in Fig. 72-

Fig. T3. Circuit Loop Break.

It consists essentially of a rigid frame with two porcelain or other suitable insulators for the sup- port of the loop wires.

Bre.]

58

[Bri.

Break-Down Switch.— (See Switch,Break- Down?)

Break-Induced Current. — (See Current, Break-Induced?)

Break, Mercury — —A form of circuit breaker operated by the removal of a conduc- tor from a mercury surface.

Mercury breaks assume a variety of forms. One end of the circuit is connected with the mercury, and the other with the conductor.

Break Shock.— (See Shock, Break\

Breaker, Circuit Any device for

breaking a circuit.

Breaking the Primary.— (See Primary, Breaking the.)

Breaking Weight of Telegraph Wires.— (See Wires, Telegraph, Breaking Weight of.)

Breath Figures. — (See Figures, Breath?)

Breeze, Electric — — A term some- times employed in electro-therapeutics for a brush discharge.

One of the electrodes, consisting of a single point or a number of points, is held near the parts to be treated so that the con vective discharge is received thereon. The other electrode is con- nected to the body of the patient.

Breeze, Electro-Therapeutic — —An

electric breeze. (See Breeze, Electric?)

Breeze, Head, Electro-Therapeutic — — A form of electric convective discharge, or electric breeze, applied to the head. (See Breeze, Electric?)

Breeze, Static — — An electric breeze obtained by the convective discharge of an electrostatic charge.

Bridge-Arms. — (See Arms, Bridge or Balance?)

Bridge, Box A box of resistance

coils so arranged as to be capable of being used directly as a Wheatstone electric balance. (See Bridge, Electric, Box Form of?)

The commercial form of Wheatstone's balance.

Bridge, Electric —A device for

measuring the value of electric resistances.

The electric bridge is also called the Electric Balance.

This is called