The Standard Electrical Dictionary - A Popular Dictionary of Words and Terms Used in the Practice - of Electrical Engineering
by T. O'Conor Slone
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[Transcriber's Notes]

Obvious spelling errors have been corrected. I have not reconciled the variety of spellings of names and other words. Obvious factual errors, typographical errors, discoveries made after 1892, and contemporary (2008) theories and use of words are noted in the text within square brackets. I have not researched and checked every assertion by the author.

This book was published 5 years before discovery of the electron. See the labored and completely inaccurate explanations of aurora and "energy, atomic". The author and his contemporaries were like fifteenth century sailors. They had a good idea of their latitude and direction (Ampere, Kirkoff, Maxwell, Gauss, Faraday, Edison, ), but only the vaguest notion of their longitude (nuclear structure, electrons, ions). Altitude (special relativity, quantum theory) was not even imagined.

Some relevant dates: Franklin's Kite—1752 Faraday's Law of Induction—1831 Maxwell's Equations—1861 Edison's Phonograph—1877 Edison's light bulb—1879 Edison's first DC power station—1882 Michelson-Morley experiment disproving ether—1887 Hertz demonstrates radio waves—1888 Westinghouse first AC power station—1891 This book—1892 Discovery of the electron—1897 Marconi radio signals cross the English Channel—1897 First Vacuum Tube—1904 Special Relativity, photo-electric effect explained with photons—1905 General Relativity: space-time dilation and curvature—1915 Confirmation of general relativity's prediction of the deflection of starlight by the Sun—1919 Discovery of the proton—1920 Quantum theory—1926 Discovery of neutron—1932 First transistor—1947 Soviet satellite Luna measures solar wind—1959 Edward M. Purcell explains magnetism with special relativity—1963

Purcell's explanation of magnetism as a result of Lorentz contraction of space along the direction of a current is a welcome relief from the convoluted descriptions in this book.

Mathematical notation is rendered using "programming" notation. ^ Power—Exponential; A^3 means "A cubed" * Multiply / Divide + Add - Subtract ( ) Precedence—Perform before enclosing expression 2E6 Scientific Notation (2,000,000)

A ——————————- 4.452 X 10^12 X t

is rendered as

A / ( 4.452E12 * t )

Where the rendering of a mathematical expression is in doubt, an image of the original text is included.

Here are some definitions absent from the text.

Foucault currents. Eddy currents.

inspissate To thicken, as by evaporation.

riband Ribbon.

sapotaceous Order Sapotace[ae] of trees and shrubs, including the star apple, the Lucuma, or natural marmalade tree, the gutta-percha tree (Isonandra), and the India mahwa, as well as the sapodilla, or sapota, after which the order is named.

Don Kostuch, MS, Electrical Engineering. [End Transcriber's notes.]


ARITHMETIC OF ELECTRICITY A MANUAL OF ELECTRICAL CALCULATIONS BY ARITHMETICAL METHODS. Third Edition. Illustrated. $1.00. It is very useful to that class of readers to whom Algebra is a comparatively unknown quantity, and will meet its wants admirably.—Electrical World.

ELECTRICITY SIMPLIFIED. A POPULAR TREATMENT OF THE SUBJECT. Illustrated. $1. 00. We especially recommend it to those who would like to acquire a popular idea of the subject.—Electric Age.






Copyright 1892 by NORMAN W. HENLEY & CO.


The purpose of this work is to present the public with a concise and practical book of reference, which it is believed will be appreciated in this age of electricity. The science has expanded so much that the limits of what may be termed strictly a dictionary of the present day would a few years ago have sufficed for an encyclopedia. It follows that an encyclopedia of electricity would be a work of great size. Yet a dictionary with adequate definitions, and kept within the closest limits by the statement of synonyms, and by the consigning of all the innumerable cross-references to a concise index will be far more than a mere dictionary in the ordinary sense of the term.

Duplication of matter is to be avoided. This makes many definitions appear short. Yet, by the assistance of the reader's own general knowledge, and by referring to the very complete index, almost any subject can be found treated in all its aspects. There are exceptions to this statement. So much has been done in the way of mechanical detail, so many inventions in telegraphy and other branches have sprung into prominence only to disappear again, or to be modified out of recognition, that to embody descriptions of many ingenious and complicated apparatus has been absolutely impossible for want of space.

A word as to the use of the book and the system of its construction may be given here. Each title or subject is defined once in the text. Where a title is synonymous with one or more others the definition is only given under one title, and the others appear at the foot of the article as synonyms. It may be that the reader is seeking the definition of one of these synonyms. If so a reference to the index shows him at once what page contains the information sought for. The use of an index in a work, necessarily of an encyclopedic form, will be appreciated by all users of this book.


Where a title embraces several words, all orders of the words will be cited in the index. To make the operation of finding references easy this rule has been carried out very fully.

It is customary to regard electricity as a growing science. It is unquestionably such, but the multiplication of terms and words is now not nearly so rapid as it has been, and the time for the compiling of a work of this character seems most propitious. It is hoped that the public will indulgently appreciate the labor it has entailed on all concerned in its production.


adj. Adjective. v. Verb. q.v. "Which see.' / A mark of division, as A/B, meaning "A divided by B." ./. The same as above. [Transcriber's note: / will be substituted for this divide symbol.] = A mark of equality, meaning "is equal to." X A mark of multiplication, meaning "multiplied by." [Transcriber's note: * will be substituted for this divide symbol.]

Fractional exponents indicate the roots expressed by their denominators and the powers expressed by their numerators. Thus, A^1/2 means the "square root of A;" A^1/3 means the "cube root of A;" B^3/2 means the "square root of the cube or third power of B."

The use of powers of ten, as 10^10, 10^11, as multipliers, will be found explained at length in the definition "Ten, Powers of."


A. Abbreviation for anode, employed in text relating to electro-therapeutics. It is sometimes written An.

Abscissa. In a system of plane co-ordinates (see Co-ordinates) the distance of any point from the axis of ordinates measured parallel to the axis of abscissas.

In the cut the abscissa of the point a is the line or distance a c.


Absolute. adj. In quantities it may be defined as referring to fixed units of quantity, and it is opposed to "relative," which merely refers to the relation of several things to each other. Thus the relative resistance of one wire may be n times that of another; its absolute resistance might be 5 ohms, when the absolute resistance of the second wire would be 5/n ohms. A galvanometer gives absolute readings if it is graduated to read directly amperes or volts; if not so graduated, it may by "calibration" q. v. be made to do practically the same thing.


Absolute Measurement. Measurement based upon the centimeter, gram, and second. (See Centimeter-Gram-Second System.)

Absolute Temperature. Temperature reckoned from absolute zero (see "Zero, Absolute"). It is obtained by adding for the centigrade scale 273, and for the Fahrenheit scale 459, to the degree readings of the regular scale.

Absorption, Electric. A property of the static charge. When a Leyden jar is being charged it dilates a little and the capacity increases, so that it can take a little more charge for a given potential difference existing between its two coatings. This phenomenon occurs with other static condensers, varying in degree with the dielectric. With shellac, paraffin, sulphur and resin, for instance, the absorption is very slight; with gutta-percha, stearine, and glass, the absorption is relatively great. The term is due to Faraday. Iceland spar seems almost or quite destitute of electric absorption.

A. C. C. Symbol of or abbreviation for "anodic closure contraction" q. v.

Acceleration. The rate of change of velocity. If of increase of velocity it is positive; if of decrease, it is negative. It can only be brought about by the exercise of force and is used as the measure of or as determining the unit of force. It is equal to velocity (L/T) imparted, divided by time (T); its dimensions therefore are L/(T^2). The c. g. s. unit of acceleration is one centimeter in one second.

[Transcriber's note: The unit of acceleration is "centimeters per second per second."]

Accumulator. (a) A term sometimes applied to the secondary or storage battery. (See Battery, Secondary.) (b) See Accumulator, Electrostatic (c) See Accumulator, Water Dropping. (d) See Wheel, Barlow's

Accumulator, Electrostatic. Two conducting surfaces oppositely placed, and separated by a dielectric and arranged for the opposite charging of the two surfaces, constitute an accumulator, sometimes termed a condenser. As this arrangement introduces the element of a bound and of a binding charge, the electrostatic capacity of such is greater than that of either or of both of its component surfaces. The thinner the dielectric which separates the conducting surfaces, and the larger the surfaces the greater is the capacity; or the less will be the potential difference which a given charge will establish between its two coatings. The nature of the dielectric also determines its capacity. (See Capacity, Specific Inductive.)



Accumulator, Water Dropping. This is also known as Sir William Thomson's Water-Gravity Electric Machine. It is an apparatus for converting the potential energy of falling water drops, due to gravity, into electric energy. Referring to the illustration, G represents a bifurcated water pipe whose two faucets are adjusted to permit a series of drops to fall from each. C and F are two metallic tubes connected by a conductor; E and D are the same. Two Leyden jars, A and B, have their inner coatings represented by strong sulphuric acid, connected each to its own pair of cylinders, B to D and E, and A to F and C. The outer coatings are connected to earth, as is also the water supply. One of the jars, say A, is charged interiorily with positive electricity. This charge, C and F, share with it, being in electric contact therewith. Just before the drops break off from the jet leading into C, they are inductively charged with negative electricity, the positive going to earth. Thus a series of negatively excited drops fall into the metal tube D, with its interior funnel or drop arrester, charging it, the Leyden jar B, and the tube E with negative electricity. This excitation causes the other stream of drops to work in the converse way, raising the positive potential of F and C and A, thus causing the left-hand drops to acquire a higher potential. This again raises the potential of the right-hand drops, so that a constant accumulating action is kept up. The outer coatings of the Leyden jars are connected to earth to make it possible to raise the potential of their inner coatings. In each case the drops are drawn by gravity into contact with objects similarly excited in opposition to the electric repulsion. This overcoming of the electric repulsion is the work done by gravity, and which results in the development of electric energy.


Acidometer. A hydrometer or areometer used to determine the specific gravity of acid. They are employed in running storage batteries, to determine when the charging is completed. (See Areometer.)

Aclinic Line. A terrestrial element; the locus on the earth's surface of no inclination of the magnetic needle; the magnetic equator. (See Magnetic Elements.)

Acoustic Telegraphy. The system of sound-reading in telegraphy, universally used in the Morse system. The direct stroke of the armature of the electro-magnet and its "back stroke" disclose to the ear the long and short strokes, dots and lines, and long and short spaces as produced by the dispatcher of the message. In the Morse system a special magnet and armature is used to produce the sound called the "sounder;" in other systems, e. g., Steinheil's and Bright's apparatus, bells are used. (See Alphabets, Telegraphic.)

Acoutemeter. A Hughes audiometer or sonometer applied to determining the quality of a person's hearing (See Hughes' Induction Balance,—Audiometer). The central coil by means of a tuning fork and microphone with battery receives a rapidly varying current tending to induce currents in the other two coils. Telephones are put in circuit with the latter and pick up sound from them. The telephones are applied to the ears of the person whose hearing is to be tested. By sliding the outer coils back and forth the intensity of induction and consequent loudness of the sounds in the telephones is varied. The position when the sounds grow so faint as to be no longer audible, gives the degree of delicacy of the person's hearing. By using a single telephone the same apparatus affords a means of testing the relative capacity of the right and left ears.


Actinic Rays. The rays of light at the violet end of the spectrum; also the invisible rays beyond such end, or the ether waves of short periods which most strongly induce chemical change.

Actinism. The power possessed by ether waves of inducing chemical change, either of decomposition or of combination. The violet and ultra-violet end of the spectrum of white light, generally speaking, represent the most highly actinic rays.

Actinometer, Electric. Properly an apparatus for measuring the intensity of light by its action upon the resistance of selenium. A current produced by fixed electro-motive force passing through the selenium affects a galvanometer more or less according to the intensity of the light. It is more properly an electric photometer. The term has also been applied to a combination of a thermo-electric pile and galvanometer, the light falling on the pile affecting the motions of the galvanometer.

Action, Local. (a) The wasteful oxydation of the zinc in a galvanic battery due to local impurities and variations in the composition of the zinc. These act to constitute local galvanic couples which cause the zinc to dissolve or oxydize, without any useful result. Amalgamation of the zinc prevents local action. Chemically pure zinc is also exempt from local action, and can be used in an acid battery without amalgamation. (See Amalgamation.)

(b) The same term has been employed to indicate the eddy or foucault currents in dynamo electric machines. (Sec Current, Foucault.)

Activity. The rate of doing work; the work done per second by any expenditure of energy. The activity of a horse-power is 550 foot lbs. per second, or 746 volt-coulombs per second. The practical electric unit is the volt-ampere, often called the watt. (Sec Energy, Electric.)

Adapter. A screw coupling to engage with a different sized screw on each end; one of the uses is to connect incandescent lamps to gas-fixtures.

A. D. C. Abbreviation for Anodic Duration Contraction, q. v.; a term in electro-therapeutics.

Adherence, Electro-magnetic. The adherence between surfaces of iron due to elcctro-magnetic attraction. It has been applied to the driving-wheels of an engine and rail, whose grip is increased by such action. In one method a deep groove was cut around the wheel which was wound with a magnetizing coil. Thus one rim becomes a north and the other a south pole, and the rail completing the circuit acts as the armature. Such an arrangement prevents a wheel from sliding. Electro-magnetic adherence has also been employed to drive friction gear wheels. In one arrangement the two wheels are surrounded by a magnetizing coil, under whose induction each attracts the other, developing high adherence between their peripheries.




Admiralty Rule of Heating. The British Admiralty specifications for the permissible heating of dynamos. It holds that at the end of a run of six hours no part of the dynamo under trial shall show a rise of temperature greater than 11 C. (20 F.) above the temperature of the air surrounding it. This is thought to be a very stringent and unnecessarily high requirement.

Aerial Conductor. An electric conductor carried from housetops, poles, or otherwise so as to be suspended in the air, as distinguished from an underground or submarine conductor.

Affinity. The attraction of atoms and in some cases perhaps of molecules for each other by the force of chemical attraction. When the affinity is allowed to act or is carried out, a chemical change, as distinguished from a physical or mechanical change, ensues. Thus if sulphur and iron are each finely powdered and are mixed the change and mixture are mechanical. If slightly heated the sulphur will melt, which is a physical change. If heated to redness the iron will combine with the sulphur forming a new substance, ferric sulphide, of new properties, and especially characterized by unvarying and invariable ratios of sulphur to iron. Such change is a chemical one, is due to chemical affinity, is due to a combination of the atoms, and the product is a chemical compound.


Agir Motor. The Anderson and Girdlestone motor. The term "agir" is made up from the first portions of each name.

Agonic Line. The locus of points on the earth's surface where the magnetic needle points to the true north; an imaginary line determined by connecting points on the earth's surface where the needle lies in the true geographical meridian. Such a line at present, starting from the north pole goes through the west of Hudson's Bay, leaves the east coast of America near Philadelphia, passes along the eastern West Indies, cuts off the eastern projection of Brazil and goes through the South Atlantic to the south pole. Thence it passes through the west of Australia, the Indian Ocean, Arabia, the Caspian sea, Russia and the White sea to the North Pole. It crosses the equator at 70 W. and 55 E. approximately. (See Magnetic Elements.)


[Transcriber's note: The file Earth_Declination_1590_1990.gif provided by the U.S. Geological Survey ( is an animation of the declination of the entire earth.]

Air. Air is a dielectric whose specific inductive capacity at atmosphere pressure is taken as 1. It is practically of exactly the same composition in all places and hence can be taken as a standard. When dry it has high resistance, between that of caoutchouc and dry paper. Dampness increases its conductivity.

It is a mixture of oxygen and nitrogen, with a little carbonic acid gas and other impurities. Its essential composition is:

Oxygen: (by weight) 23.14 (by volume) 21 Nitrogen: 76.86 79

The specific inductive capacity varies for different pressures thus:

Approximate vacuum (.001 mm., .0004 inch) 0.94 (Ayrton) " " ( 5 mm. , .2 inches ) 0.9985 (Ayrton) 0.99941 (Boltzman.)

The specific gravity of air under standard conditions 15.5 C (60 F.) and 760 mm. barometric pressure (30 inches) is taken as unity as a standard for gases.

[Transcriber's note: Argon accounts for 0.9340%. It was discovered in 1894, two years after this book.]

Air-Blast. (a) In the Thomson-Houston dynamo an air-blast is used to blow away the arc-producing spark liable to form between the brushes and commutator. It is the invention of Prof. Elihu Thomson. The air is supplied by a positive action rotary blower connected to the main shaft, and driven thereby. The wearing of the commutator by destructive sparking is thus prevented.

A drum H H is rotated, being mounted on the axis X of the dynamo. As it rotates the three vanes are thrown out against the irregular shaped periphery of the outer case T T. The arrow shows the direction of rotation. The air is thus sent out by the apertures a a. O is the oil-cup.

(b) The air-blast has also been used by Prof. Thomson in experiments with high frequency currents of high potential. By directing a blast of air against a spark discharge between ball terminals of an alternating current, the nature of the current was changed and it became capable of producing most extraordinary effects by induction.



Air Condenser. A static condenser whose dielectric is air. The capacity of an air condenser in farads is equal to A / ( 4.452E12 * t ) in which A is the area of one sheet or sum of the areas of one set of connected sheets in square inches and t is the thickness of the layer of air separating them.

A convenient construction given by Ayrton consists in a pile of glass plates P separated by little bits of glass F of known thickness, three for each piece. Tin-foil T is pasted on both sides of each piece of glass and the two coatings are connected. The tin-foil on each second plate is smaller in area than that on the others. The plates are connected in two sets, each set comprising every second plate. For A in the formula the area of the set of smaller sheets of tin-foil is taken. By this construction it will be seen that the glass does not act as the dielectric, but only as a plane surface for attachment of the tin-foil. Posts E E keep all in position. One set of sheets connects with the binding post A, the other with B.

The capacity of any condenser with a dielectric of specific inductive capacity i is given by the formula: ( i *A^1 ) / ( 4.452E12 * t1 )

The air condenser is used for determining the value of i for different dielectrics.



Air Gaps. In a dynamo or motor the space intervening between the poles of the field magnet and the armature. They should be of as small thickness, and of as extended area as possible. Their effect is to increase the magnetic reluctance of the circuit, thereby exacting the expenditure of more energy upon the field. They also, by crowding back the potential difference of the two limbs, increase the leakage of lines of force from limb to limb of the magnet.

Air Line Wire. In telegraphy the portion of the line wire which is strung on poles and carried through the air.

Air Pump, Heated. It has been proposed to heat portions of a mercurial air pump to secure more perfect vacua, or to hasten the action. Heating expands the air and thus produces the above effects.


Air Pump, Mercurial. An air pump operated by mercury. The mercury acts virtually as the piston, and the actuating force is the weight of the column of mercury, which must exceed thirty inches in height. There are many types. Mercurial air pumps are largely used for exhausting incandescent lamp chambers. (See Geissler Air Pump,—Sprengel Air Pump.)

Air Pumps, Short Fall. A mercurial air pump in which the fall of mercury or the height of the active column is comparatively small. It is effected by using several columns, one acting after the other. A height of ten inches for each column suffices in some forms. Enough columns must be used in succession to make up an aggregate height exceeding 30 inches.



Alarm, Burglar. A system of circuits with alarm bell extending over a house or apartments designed to give notice of the opening of a window or door. As adjuncts to the system the treads of the stairs are sometimes arranged to ring the bell, by completing a circuit when trod on. Door mats are also arranged to close circuits in like manner.


For doors and windows switches are provided which are open as long as the door or window is closed, but which, on being released by opening the door or windows, automatically close the circuit. The circuit includes an alarm bell and battery, and the latter begins to ring and continues until stopped, either by the closing of the door or by a switch being turned. The connections are sometimes so contrived that the reclosing of the door or window will not stop the bell from ringing.

The cuts show various switches for attachment to doors and windows. It will be seen that they normally keep the circuit closed, and that it is only open when pressure, as from a closed door, is brought upon them. In the case of a door a usual place for them is upon the jamb on the hinge side, where they are set into the wood, with the striking pin projecting, so that as the door is closed the pin is pressed in, thus breaking the circuit.

Sometimes the connections are arranged so as to switch on the electric lights if the house is entered. Special annunciators showing where the house has been entered are a part of the system. A clock which turns the alarm on and off at predetermined hours is also sometimes used.

The circuits may be carried to a central station or police station. One form of burglar alarm device is the Yale lock switch. This is a contact attached to a Yale lock which will be closed if the wrong key is used, completing a circuit and ringing a bell.


Alarm, Electric. An appliance for calling attention, generally by ringing a bell. It is used to notify of water-level in boilers or tanks, of entrance of a house, or of other things as desired. It is evident that any number of alarms could be contrived.


Alarm, Fire and Heat. An alarm for giving notice of the existence of a conflagration. Such are sometimes operated by a compound bar thermostat (see Thermostat), which on a given elevation of temperature closes a circuit and rings an electric bell. Sometimes the expansion of a column of mercury when heated is used. This, by coming in contact with one or two platinum points, completes a circuit, and rings the bell.

The identical apparatus may be used in living rooms, greenhouses. factories and elsewhere, to give an alarm when the temperature rises or falls beyond predetermined limits.

Alarm, Overflow. An alarm to indicate an overflow of water has been suggested on the lines of a contact completed by water, or of the elements of a battery which would be made active by water. Thus two sheets of metal might be separated by bibulous paper charged with salt. If these sheets were terminals of a circuit including a bell and battery, when water reached them the circuit would be closed and the bell would ring. It was also proposed to use one copper and one zinc sheet so as to constitute a battery in itself, to be thrown into action by moisture. These contacts or inactive batteries could be distributed where water from an overflow would be most likely to reach them.

Alarm, Water Level. An alarm operated by a change of water level in a tank or boiler. By a float a contact is made as it rises with the water. Another float may be arranged to fall and close a contact as the level falls. The closing of the contacts rings an electric bell to notify the attendant in charge.

Alcohol, Electrical Rectification of. A current of electricity passed through impure alcohol between zinc electrodes is found to improve its quality. This it does by decomposing the water present. The nascent hydrogen combines with the aldehydes, converting them into alcohols while the oxygen combines with the zinc electrode.

Alignment. The placing in or occupying of the same straight line. The bearings of a shaft in dynamos, engines, and other machinery have to be in accurate alignment.

Allotropy. The power of existing in several modifications possessed by some substances, notably by chemical elements. Instances of the allotropic state are found in carbon which exists as charcoal, as graphite (plumbago or black lead), and as the diamond. All three are the same elemental substance, although differing in every physical and electrical property.


Alloy. A mixture, produced almost universally by fusion, of two or more metals. Sometimes alloys seem to be chemical compounds, as shown by their having generally a melting point lower than the average of those of their constituents. An alloy of a metal with mercury is termed an amalgam. An important application in electricity is the use of fusible alloys for fire alarms or for safety fuses. German silver is also of importance for resistance coils, and palladium alloys are used for unmagnetizable watches. An alloy of wrought iron with manganese is almost unmagnetizable, and has been proposed for use in ship building to avoid errors of the compass.

Alloys or what are practically such can be deposited by electrolysis in the electro- plater's bath. We give the composition of some alloys interesting to the electrician.

Solder: Lead 1 part Tin 2 parts " " " 1 " " " " 2 "

German Silver: Copper, 2 parts; Nickel, 1 part; Zinc, 1 part (used for resistances).

Platinum, Silver Alloys: Platinum, 1 part; silver, 2 parts (used for resistances.)

Palladium alloys for watch springs. (See Palladium.)

Alphabet, Telegraphic. The combinations of sounds, of dots and dashes marked on paper, of right-hand and left-hand deflections of a needle, of bells of different notes, or of other symbols by which a fixed combination is expressed for each character of the alphabet, for numerals, and for punctuation. While the code is designed for telegraphic uses it can be used not only for the conveyance of signals and messages by the electrical telegraphs, but also by any semaphoric or visual system, as by flashes of light, movements of a flag or even of the arms of the person signalling.

In the English and continental needle telegraphy in which the message is transmitted by the movements of an index normally vertical, but oscillating to one side or the other under the influence of the current, the latter being controlled by the transmitter of the message, the left hand swings of the needle are interpreted as dots, the right hand as dashes.

This system enables one alphabet to be translated into the other, or virtually one alphabet answers for both Morse and needle transmitters.

There are two principal telegraphic alphabets, the American Morse and the International codes. They are very similar, their essential distinction being that spaces are used in the American code, while they are excluded from the International code.

In the American Morse system the message is now universally received by sound. (See Sounder—Sound Reading.)


The two codes or telegraphic alphabets are given here.

THE INTERNATIONAL ALPHABET. Parenthesis, - . - - . - Understand, ... - . I don't understand, ..— ....—.. Wait, .-. . . Erase, ... ... ... Call signal, -.-.-.- End of message, .-.-.-. Cleared out all right, .-..-..-. A .- L .-.. W .— B -... M — X -..- C -.-. N -. Y -.— D -.. O —- Z —.. E . P .—. F ..-. Q —.- Ch —— G —. R .-. .-.- H .... S ... —-. I .. T - ..— J .—- U ..- ..-.. K -.- V ...- —.—

NUMERALS 1 .—— 4 ....- 8 —-.. 2 ..—- 5 ..... 9 ——. 3 ...— 6 -.... 0 ——- 7 —...

[Transcriber's note: The original image of the dot/dash pattern is somewhat ambiguous. Since there may be differences from contemporary specifications, the original image is included.]




Period (.) ... ... Comma (,) .-.-.- Query(?) ..—.. Exclamation (!) —..— Apostrophe (') .——. Hyphen (-) -....- Fresh paragraph, .-.-.. Inverted commas, -..-.

THE AMERICAN ALPHABET. A .- L ——(Continuous) W .— B -... M — X .-.. C ..s. N -. Y ..s.. D -.. O .s. Z . E . P ..... F .-. Q ..-. Ch —— G —. R .s.. .-.- H .... S ... —-. I .. T - ..— J - . - . U ..- ..-.. K -.- V ...- —.—

NUMERALS 1 .—. 4 ....- 8 -.... 2 ..-.. 5 —- 9 -..- 3 ...-. 6 ... ... 0 ——-(Continuous) 7 —..

[Transcriber's Note: The "s" in the American Code indicates a "space". I leave the following to the reader's imagination. See the original image.]

Comma (,) Semicolon (;) Colon (:) Colon Dash (:~) Period (.) Interrogation (?) Exclamation (!) Dash (-) Hyphen (-) Pound Sterling () Shilling Mark ( )

[Image of page 21: THE AMERICAN ALPHABET.]


[Transcriber's Note: I leave these to the reader's imagination. See the following original image.]

Dollars ($) Decimal Point (.) Cents (c) Paragraph () Pence (d.) Fractional Mark (—) Capitalized Letter Italics or Underline Colon followed by Quotation :" Parenthesis ( ) Brackets [ ] Quotation Marks " " Quotation within a Quotation " ' ' "

[Image of page 22: THE AMERICAN ALPHABET.]

The principal differences in the two codes are the use of spaces in the American code, such being excluded from the International code. This affects the letters C, R, Y, & Z.

The following diagram, due to Commandant Perian, enables the letter corresponding to an International code sign to be rapidly found with the exception of R.

/ E T / / I A N M / / / / S U R W D K G O / / / / / / / / H V F U L A P J B X C Y Z Q CH

Fig. 10. Diagram for translating the Morse Alphabet.

In order to find what letter corresponds to a given sign, starting from the top of the diagram, each line is traced down to a bifurcation, taking the right hand line of each bifurcation for a dash, and the left hand line for a dot, and stopping when the dots and dashes are used up. Thus, for example,

the signal -.- - leads us to the letter d,

the signal - - - - to the letter j and so on.


Alternating. adj. Term descriptive of a current changing periodically in direction. (See Current, Alternating.)


Alternating Current Arc. The arc produced by the alternating current. It presents several peculiarities. With an insufficient number of alternations per second it goes out. As the carbons wear away equally it is adopted for such lamps as the Jablochkoff candle, (see Candle, Jablochkoff). As no crater is formed the light is disseminated equally both up and down. For this reason to get full downward illumination a reflector is recommended.

Alternating Current System. A system of electric distribution employing the alternating current. For transmission in the open air or in conduits a high potential circuit is used, from 1,000 to 10,000 volts being maintained at the central station. Two leads unconnected at the end lead from the station. Where current is desired a converter or transformer (see Converter) is placed, whose primary is connected to the two leads bridging the interval between them. From the secondary the house leads are taken with an initial potential in some cases of 50 volts. The converters are thus all placed in parallel. By law or insurance rules the converters are generally kept outside of buildings. Where no secondary current is taken from the converters very little primary current passes them on account of their counter-electromotive force. As more secondary current is taken the primary increases and this accommodation of one to the other is one of the interesting and valuable features. Street lamps are sometimes connected in series. Each lamp in such case is in parallel with a small coil with iron core. While the lamp is intact little current passes through the coil. If the lamp is broken, then the converter impedes the current by its spurious resistance, q. v., just enough to represent and replace the resistance of the extinguished and broken lamp filament. (See Meter, Alternating Current; Motor, Alternating Current.)

Alternation. The change in direction of a current. The number of such changes is expressed as number of alternations; thus a current may have a frequency of 500 or 20,000 alternations per second.

[Transcriber's note: One alternation per second is now called one hertz.]

Alternation, Complete. A double alternation; a change from one direction to the other and back again to the original phase. A symbol derived from its graphic representation by a sine curve is used to indicate it. The symbol is ~


Alternative Path. A second path for a current appearing as a disruptive discharge. Where two paths are offered the discharge, as it is of alternating or oscillatory type, selects the path of least self-induction. Thus a thick bar of copper, with no air gap, may be abandoned by the current in favor of a small iron wire with an air gap, but which has less self-induction.

The lightning arresters, q. v., for the protection of telegraph offices are sometimes based on these principles. A path of very high resistance but of small self-induction is offered between the line and the earth. This the lightning discharge selects in preference to the instruments with their iron cores, as the latter are of very high self-induction.

Alternator. A dynamo electric generator supplying an alternating current. (See Dynamo, Alternating Current.)

Synonym—Alternating current generator or dynamo.

Alternator, Constant Current. An alternating current dynamo supplying a current of unvarying virtual amperage. Alternators of this type are constructed with an armature of high self-induction. Sometimes fine winding contained in deep peripheral notches in the core-discs is employed to magnify the self-induction. Such generators are employed for series lighting, especially arc-lighting.

Aluminum. A metal; one of the elements; symbol: Al. Atomic weight: 27.4. Equivalent: 9.13. Valency: 3. Specific gravity: 2.6. It is a conductor of electricity. Relative resistance annealed, (Silver = 1) 1.935 Specific resistance at 0C (32F.) 2.912 microhms

Resistance of a wire at 0C (32F.) a) 1 foot long, weighing 1 grain, 0.1074 ohms. b) 1 foot long, 1/1000 inch thick, 17.53 " c) 1 meter long, weighing 1 gram, 0.0749 " d) 1 meter long, 1 millimeter thick 0.03710 " Resistance of a 1-inch cube at 0C (32F.) 1.147 microhms Electro-chemical equivalent. .0958 (hydrogen == .0105)


Amalgam. (a) A combination or alloy in which one of the constituents is mercury. Usually the term is applied to an alloy of a single metal with mercury. Some metals readily form amalgams; such metals are: Gold, zinc, silver, lead and others; some, such as platinum and iron, form amalgams only under exceptional circumstances.

(b) The word is also applied to compositions for application to the cushions of frictional electric machine in which cases it is often a misnomer. True amalgams used for this purpose are made as follows:

(a) Tin, 1 part; Zinc, 1 part; Mercury, 2 parts (Kienmayer). (b) Tin, 2 parts; Zinc, 3 parts. (c) Tin, 3 parts; Zinc, 5 parts; Mercury, 4 parts. (d) Zinc, 1 part: Mercury, 4 parts; Mercury, 9 parts. [sic]

The tin, if such is used, (formula a, b and c) is first melted, the zinc is added in successive portions. The mercury, which must be heated, is slowly poured into the melted alloy after removal of the latter from the fire, and the mixture, while making, is constantly stirred. It is kept stirred or rubbed in a mortar until cold. Sometimes it is poured into water and kept in constant agitation until cold. It is thus obtained in a granular condition, and is pounded in a mortar until reduced to powder. It must be dried and kept in tightly stopped bottles and is applied to the cushions after they have been greased. It is to be noticed that it is said that alloy (d) requires no pulverization beyond constant rubbing in a mortar as it cools. Sometimes the amalgam is shaken about in a wooden tray with chalk while cooling. The action of amalgams is not very clearly understood. Some claim that there is a chemical action, others that they simply act as conductors, others that they are more highly negative to the glass than the leather of the cushions.

Graphite or sulphide of tin (mosaic gold) are sometimes used to coat the cushions; it is these that are sometimes incorrectly called amalgams.

Amalgamation. The application of mercury to a metal with which it forms an amalgam, or with which it amalgamates. Battery zincs are amalgamated in two ways. In the immersion method, the plate is dipped into an acid solution of mercuric chloride or nitrate. The latter is best. In the direct application method the plate is first wet all over with dilute acid and a little mercury is dropped upon it and is rubbed over the surface with a rag or, what is better, with a piece of galvanized iron. A very little mercury answers the purpose. The whole surface of the plate should be left as bright as silver. (See Action, Local.)

Amber. Amber is a fossil resin, supposed to be a product of the extinct Pinites Succinifer and other coniferous trees. Most of it is gathered on the shores of the Baltic between Koenigsberg and Memel. It is also found in small pieces at Gay Head, Mass., and in New Jersey green sand. It is found among the prehistoric remains of the Swiss Lake dwellers. When rubbed with a cloth it becomes excited with negative electricity. The Greek word for it is electron, which gave the name electricity to the modern science. Thales of Miletus, 600 B. C., and Theophrastus, about 300 B. C., both mention its electric properties or power of attracting small objects when rubbed.


Ammeter. The commercial name for an ampere-meter, an instrument designed to show by direct reading the number of amperes of current which are passing through a circuit.

A great variety of ammeters have been invented, based on different principles. The definitions following this one give some idea of the lines of construction followed.

Synonym—Ampere meter.

Ammeter, Ayrton's. A direct reading instrument for measuring current intensity.

A solenoid receives the current. In the axis of the solenoid an iron tube is suspended by a long spiral spring that passes down within it, and the upper end of which spring is fastened to the glass top of the instrument. The tube is provided with proper guides so as to maintain a vertical position, and is free to rotate. Its upper end carries an index.

The whole operates as a magnifying device. A slight longitudinal displacement of the tube causes it to rotate through a considerable angle by the action of the spring. By properly proportioning the parts, the angle of displacement of the index is directly proportional to the current between 15 and 270 angular displacement.

The same instrument is wound for use as a volt-meter.

Its principal fault is its restricted range.

Ammeter, Commutator. A commutator ammeter is one whose windings consist of separate strands, each of any desired number of turns, and provided with a commutating attachment for throwing them into series or into parallel as desired. The essential condition is that all the wires shall be of equal resistance and of equal number of turns. Such an instrument can be used for heavy or light currents. Two sets of graduations are marked on its scale if it is a calibrated instrument. (See Calibration.) Commutator volt-meters are constructed on the same principle.

Ammeter, Cunynghame's. A modification of the Siemens' electro-dynamometer. (See Electro-dynamometer, Siemens'.) An electro-magnet with very massive core is excited by the current. As the core is of small reluctance the strength of the magnet is nearly proportional to the current strength. Between the poles of the magnet a soft iron armature or induced magnet is pivoted. It carries a pointer so adjusted that when the axis of the soft iron magnet is at an angle of about 30 with the line joining the poles of the electro-magnet the pointer will indicate zero.

The soft iron armature is so massive that the magnetism induced in it is proportional to the strength of the electro-magnet. Hence the couple exerted by the electro-magnet on the pivoted armature will be proportional to the square of the current.

The armature is retained in place by a spiral spring lying in line with its axis of rotation. The instrument is operated as a zero reading instrument. The current is passed through it. The needle is deflected; it is brought back to zero by turning a milled head which twists the spring. The current will be proportional to the square root of the angle of displacement of the milled head. A scale with index is provided, giving directly the square roots of the angle over which the pointer is moved.

The same instrument is wound for use as a volt-meter.


Ammeter, Eccentric Iron Disc. This ammeter comprises a cylindrical electro-magnet excited by the current to be measured. A disc of iron free to rotate is suspended on pivots below it. A piece is cut off the disc at one part of its periphery so as to give more metal to one side than to the other. In its zero position this portion of the disc swings towards the magnet. As the latter is more and more excited the other or more projecting portion of the disc turns towards it, being attracted like an armature, and moves against the force of gravity, the disc rotating. An index attached to the disc swings over the face of a graduated scale. The disc is so counterpoised that in its natural position the index points to zero.

Ammeter, Electro-magnetic. An ammeter depending for its working upon the action of an electro-magnet, which is excited by the current to be measured.

Ammeter, Gravity. An ammeter whose hand or index is drawn into the zero position by gravity, and whose displacement therefrom is produced by the action of the current to be measured.


Ammeter, Magnetic Vane. A fixed plate of soft iron is placed within a coil. Facing it is a second disc free to move or swing on an axis. When the field is excited the two repel each other because like polarity is induced in each, and the motion of the movable disc indicates the strength of the current. The same instrument is wound for high resistance and constitutes a Magnetic Vane Voltmeter.


Ammeter, Magnifying Spring. A solenoid ammeter in which a spiral spring is used to convert the longitudinal motion of the armature or movable core into a rotary motion (see Ammeter, Ayrton's) and magnify the apparent range of motion.

Ammeter, Permanent Magnet. An ammeter with a magnetic field produced by a permanent magnet.

Ammeter, Solenoid. An ammeter in which the attraction, when a current is passing through it, exerted by a hollow coil of wire upon an iron bar or tube in line with its axis, is utilized to indicate the strength of current. The bar is drawn into the coil to different extents proportional to the attraction. As an example see Ammeter, Ayrton's, and cut of Gravity Ammeter.

Ammeter, Spring. An ammeter in which the part moved by the current is controlled or brought to the zero position by a spring.

Ammeter, Steel Yard. A solenoid ammeter in which the solenoid core is suspended vertically from the short end of a steel yard fitted with a sliding weight. The current passes through the solenoid coil and attracts or draws downwards the coil. A sliding weight is moved in and out on the long steel-yard arm which is graduated for amperes. In use the weight is slid out until the arm is in equipose; the divisions give the amperes.



Ammunition Hoist, Electric. An apparatus for use on ships for hoisting ammunition to the guns by an electric elevator. The characteristic feature of it is that a constant motion of the switch or handle is required to keep it in action. If the operator is shot so as to be incapacitated from taking charge of the switch, the hoist stops until another is assigned to it.

Amperage. Current intensity expressed in amperes, as an amperage of ten amperes.

Ampere. The practical unit of electric current strength. It is the measure of the current produced by an electro-motive force of one volt through a resistance of one ohm. In electric quantity it is the rate of one coulomb per second. It is one-tenth the absolute C. G. S. unit of current strength. Its best analogy is derived from water. Assuming the electric current to be represented by a current of water, the pressure, head, or descent producing such current would be the electro-motive force. The current might be measured in gallons (or other unit) passed per second. In the analogy these gallons would be coulombs. But it might be measured by reference to a standard stream, as for instance, the stream which would pass through a hole an inch square under a given head, say six inches of water. This unit is the miner's inch, and is the exact analogy of the ampere. A current of water may flow at the rate of so many miner's inches, just as a current of electricity may flow at the rate of so many amperes. In neither case it will be noted is there any reference to time. "An ampere per second" is a redundant expression, and means no more than "an ampere"; an "ampere-second," on the other hand, is a coulomb. The number of coulombs passed per second gives the amperes of current.

For value of ampere, see Coulomb.

[Transcriber's note: The SI definition of an ampere: A current in two straight parallel conductors of infinite length and negligible cross-section, 1 metre apart in vacuum, would produce a force equal to 2E-7 newton per metre of length.]



Ampere, Arc. A conductor bent into the arc of a circle, and employed in measuring the electric current by the electric balance.

Ampere-currents. The currents assumed to be the cause of magnetism. (See Magnetism, Ampere's Theory of.)

Ampere-feet. The product of amperes of current by the length, in feet, of a conductor passing such current. It may be in empiric calculations of dynamo or motor construction, but is little used. One ampere-foot is a current of one ampere passing through one foot length of a conductor, or one-tenth ampere through ten feet, and so on.

Ampere-hour. The quantity of electricity passed by a current of one ampere in one hour. It is used by electric power and lighting companies as the unit of energy supplied by them, because they maintain a constant potential difference in their leads, so that only the amperes and hours need measuring or recording to give the energy, viz. : volt-ampere-hours. The same unit is applied to batteries to indicate their potential energy, because they also are assumed to be of constant voltage or electro-motive force.

Ampere-meters. The product of amperes of current by the length, in meters, of a conductor carrying such current. One ampere-meter is a current of one ampere passing through one meter of a conductor.

The term must not be confused with the identically spelled Ampere-meter, a synonym for Ammeter.

Ampere-minute. The quantity of electricity passed by a current of one ampere in one minute; sixty coulombs.

Ampere Ring. A conductor forming a ring or circle used in electric balances for measuring currents. (See Balance, Ampere.)

Ampere-second. The quantity of electricity passed by a current of one ampere in one second; the coulomb, q. v.

Amperes, Lost. In a shunt or compound-wound dynamo, part of the total amperes of current produced in the armature coils go through the shunt, and hence, do not appear in the outer circuit. S. P. Thompson has proposed the term "lost amperes" for this portion of the current.

Ampere's Memoria Technica. An expression of the effect of a current on a magnetic needle. If we imagine the observer in the line of the current and facing the magnetic needle, the current entering by his feet and leaving by his head, the north pole is deflected to his left.


Ampere-turns. The amperes of current supplied to a magnet coil multiplied by the number of turns the current makes in the coil. If the coil is wound two or three in parallel, the virtual turns by which the amperes are multiplied are one-half or one-third the actual turns of wire.

Synonym—Ampere Windings.

Ampere-turns, Primary. The ampere-turns in the primary coil of an induction coil or transformer.

Ampere-turns, Secondary. The ampere-turns in the secondary coil of an induction coil or transformer.

Amplitude of Waves. Waves are distinguished by length and amplitude. The latter, in the case of transverse waves, such as those of water and of the ether, correspond with and measure the height from lowest to highest point, or from valley to summit of the waves in question. In the case of longitudinal waves, such as those of the air, due to sounding bodies, the ratio of degree of rarefaction to degree of condensation existing in the system is the amplitude. The latter can be graphically represented by a sinuous line, such as would represent the section of a transverse wave. Ether waves are produced by heated bodies and by electro-magnetic impulses, as in the discharge of the Leyden jar.

The amplitude of a wave, other things being equal, is the measure of its intensity. Thus, the louder a sound the greater is the amplitude of the system of waves to which it is due. The same applies to ether waves, whether they are perceived in the electro-magnetic, light, or heat-giving modification. As the amplitude of ether waves cannot be accurately known, amplitude is a relative term and is not stated generally in any absolute unit.

Analogous Pole. One of the elements of a pyro-electric crystalline substance, such as tourmaline. When heated, such bodies acquire electrical properties. If of such crystalline form that they are differently modified at the ends of their crystalline axis, by hemihedral modifications, the ends may be differently affected. One end may show positive electricity when the temperature is rising, and negative when falling. Such end is then called the analogous pole. The opposite end presents, in such cases, the opposite phenomena; becoming negative when the temperature is rising, and becoming positive when it is falling; such end is called the antilogous pole.

Analysis. The determination of the elements of a case. It may be chemical, and consist in finding what a substance consists of; it may be mathematical, and consist in determining the unknown quantities in a problem; or it may belong to other branches of science. The term has a very extended application. Where the constituents are only determined in kind it is called qualitative analysis; where their quantity or percentage is ascertained it is called quantitative analysis.


Analysis, Electric. Chemical analysis by electrolytic methods. (See Electrolytic Analysis.)

Analyzer, Electric. An apparatus used in investigations on electric ether waves. It consists of a series of parallel metallic wires. When the electric waves have been polarized, the analyzer will only permit them to go through it intact, when the plane of vibration of the waves is parallel to its wires.

Anelectrics. (a) Bodies which do not become electrified by friction; a term introduced by Gilbert, now little used, as all bodies develop electricity under proper conditions by contact action; the reverse of idioelectrtics.

(b) Also a conductor of electricity, the reverse of a dielectric, q. v. (See Conductor.)

It will be seen that Gilbert's anelectrics were, after all, the same as the modern anelectrics, i.e., conductors.

Anelectrotonus. A term used in medical electricity or electro-therapeutics to indicate the deceased functional activity induced in a nerve by the proximity of the anode of an active electric circuit completed through the nerve. The converse of Kathelectrotonus.

Angle of Declination. The angle of error of the magnetic needle or compass, measuring the extent of its deviation from the meridian in any locality. It is the angle between the plane of the magnetic axis of a magnetic needle free to take its natural position, and the geographical meridian, the needle being counterpoised if necessary, so as to hold an absolutely horizontal position. The deviation is expressed as being east or west, referring always to the north pole. (See Magnetic Elements.)

Synonym—Variation of the Compass.

[Transcriber's note: See Agonic Line.]

Angle of the Polar Span. In a dynamo or motor the angle subtended by the portion of a pole piece facing the armature, such angle being referred to the centre of the cross-section of the armature as its centre.


Angular Velocity. The velocity of a body moving in a circular path, measured with reference to the angle it passes over in one second multiplied by the radius and divided by the time. A unit angle is taken (57.29578 = 57 17' 44".8 nearly) such that it is subtended by a portion of the circumference equal in length to the radius. Hence, the circumference, which is 360, is equal to 2*PI*unit angle, PI being equal to 3.1416—. "Unit angular velocity" is such as would in a circle of radius = 1 represent a path = 1, traversed in unit time = 1 second. If the radius is r and the angle passed over is theta, the distance is proportional to r*theta; if this distance is traversed in t seconds the angular velocity is theta / t. The angular velocity, if it is multiplied by r, theta expressing a distance, will give the linear velocity. The dimensions of angular velocity are an angle (= arc / radius) / a Time = (L/L)/T = (T^-1).

The velocity expressed by the rate of an arc of a circle of unit radius, which arc subtends an angle of 57 17' 44".8, such arc being traversed in unit time, is unit angular velocity.

Animal Electricity. Electricity, notably of high tension, generated in the animal system, in the Torpedo, Gymnotus and Silurus. The shocks given by these fish are sometimes very severe. The gymnotus, or electric eel, was elaborately investigated by Faraday. It has the power of voluntarily effecting this discharge. There is undoubtedly some electricity in all animals. The contact of the spinal column of a recently killed frog with the lumbar muscles produces contraction, showing electric excitement. Currents can be obtained from nerve and muscle, or from muscle sides and muscle cut transversely, in each case one thing representing positive and the other negative elements of a couple.

Angle of Inclination or Dip. The angle which the magnetic axis of a magnet, which magnet is free to move in the vertical plane of the magnetic meridian, makes with a horizontal line intersecting such axis. To observe it a special instrument, the dipping compass, inclination compass, dipping needle, or dipping circle, as it is called, is used. (See Elements, Magnetic, —Dipping Needle,—Compass, Inclination.)

Angle of Lag. The angle expressing the displacement of the magnetic axis of the armature core of a dynamo in the direction of its rotation. (See Lag.) Lag is due to the motion of the armature core.

Angle of Lead. The angle expressing the displacement in the direction of rotation of the armature of a dynamo which has to be given the brushes to compensate for the lag. (See Lag.) This is positive lead. In a motor the brushes are set the other way, giving a negative angle of lead or angle of negative lead.

Anion. The electro-negative element or radical of a molecule, such as oxygen, chlorine or the radical sulphion. (See Ions.) It is the portion which goes to the anode, q.v., in electrolytic decomposition.


Anisotropic. (adj.) Unequal in physical properties, as in conduction and specific inductive capacity, along various axes or directions. An anisotropic conductor is one whose conductivity varies according to the direction of the current, each axis of crystallization in a crystalline body marking a direction of different conductivity. An anisotropic medium is one varying in like manner with regard to its specific inductive capacity. In magnetism an anisotropic substance is one having different susceptibilities to magnetism in different directions. The term is applicable to other than electric or magnetic subjects.


Annealing, Electric. Annealing by the heat produced by the passage of the electric current through the body to be annealed. The object is clamped or otherwise brought into a circuit, and a current strong enough to heat it to redness, or to the desired temperature is passed through it.

Annunciator. An apparatus for announcing a call from any place to another, as from a living-room to an office in a hotel, or for announcing the entering of any given room or window in a building protected by a burglar alarm.

A usual system comprises for each annunciator an electro-magnet. Its armature is normally held away from its poles by a spring, and when in that position a latch connected to the armature holds a little shutter. When by a push-button or other device a current is sent through a circuit which includes the electro-magnet the armature is attracted, this releases the latch and the shutter drops. In dropping it displays a number, letter or inscription which indicates the locality of the push-button or other circuit-closing device. Often annunciators are connected in circuit with a bell.



Annunciator Clock. A clock operating an annunciator by making contact at determined times.

Annunciator Drop. The little shutter which is dropped by some forms of annunciators, and whose fall discloses a number, character or inscription, indicating whence the call was sent.



Annunciator, Gravity Drop. An annunciator whose operations release shutters which fall by gravity.

Annunciator, Needle. A needle annunciator is one whose indications are given by the movements of needles, of which there is usually a separate one for each place of calling.

Annunciator, Swinging or Pendulum. An annunciator which gives its indications by displacing from its vertical position a pendulum or vertically suspended arm.


Anodal Diffusion. A term in electro-therapeutics; the introduction of a medicine into the animal system by using a sponge-anode saturated with the solution of the drug in question. On passing a current the desired result is secured by cataphoresis, q. v.

Anode. The positive terminal in a broken metallic or true conducting circuit; the terminal connected to the carbon plate of a galvanic battery or to its equivalent in case of any other generator. In general practice it is restricted to the positive terminal in a decomposition or electrolytic cell, such as the nickel anode in a nickel-plating bath or the anode of platinum in a gas voltameter. It is the terminal out of or from which the current is supposed to flow through the decomposition cell. In electro-therapeutics the term is used simply to indicate the positive terminal. In an electrolytic cell the electro-negative substance or anion goes to the anode. Hence, it is the one dissolved, if either are attacked. The nickel, copper or silver anodes of the electroplater dissolve in use and keep up the strength of the bath. The platinum anode in a gas voltameter is unattacked because the anion cannot act upon it chemically.

Anodic Closure Contraction. A physiological change in a living subject produced by the closing of the electric current; the muscular contraction which takes place beneath the anode applied to the surface of the body when the circuit is closed, the kathode being applied elsewhere; it is due, presumably, to direct action on the motor nerve. It is a term in electro-therapeutics. It is the converse of anodic opening contraction, q. v. An abbreviation A. C. C. is often used to designate it.

Anodic Duration Contraction. A term in electro-therapeutics. On the opening or closing of an electric circuit, the anode of which is placed over a muscle, a contraction is observed (see Anodic Closure Contraction—Anodic Opening Contraction). The above term is used to designate the duration of such contraction. An abbreviation A. D. C. is often used to designate it.

Anodic Opening Contraction. The converse of Anodic Closure Contraction, q. v.; it is the contraction of living muscle beneath or near the anode where the circuit, including such anode and the body in its course, is closed; a physiological phenomenon observed in electro-therapeutics to which branch of science the term belongs. An abbreviation A. O. C. is often used to designate it.

Anodic Reactions. A term in electro-therapeutics; the diagnosis of disease by the actions of the tissue near the anode of a circuit.

Anti-Induction Conductor. A conductor constructed to avoid induction effects in the conducting element. Many kinds have been made. A tubular metal shield or envelope which may be grounded will protect an enclosed conductor to some extent. Or the conductor may be a double wire twisted around itself, one branch being used for the regular and the other for the return circuit, thus constituting a closed metallic circuit. The inductive effects are due to interrupted or varying currents in neighboring wires and circuits. Many anti-induction conductors have been invented and patented.


Anti-magnetic Shield. In general terms a hollow screen of soft iron designed to protect any mass of steel behind or enclosed by it from magnetization by any magnet near it, such as a dynamo field magnet. This it does by concentrating the lines of force within its own mass, so that the space within it or enclosed by it is comparatively free from lines of force. It is often applied to watches, and is virtually an iron case in which they are enclosed.

Antimony. A metal, one of the elements, atomic weight, 122: equivalent, 40.6 and 24.4; valency, 3 and 5; specific gravity, 6.8. It is a conductor of electricity. Relative resistance, compressed (silver = 1), 23.60 Specific resistance, 35.50 microhms. Resistance of a wire, (a) 1 foot long, weighing 1 grain, 3.418 ohms. (b) 1 foot long, 1/1000 inch thick, 213.6 " (c) 1 meter long, weighing 1 gram, 2.384 " (d) 1 meter long. 1 millimeter thick, 0.4521 "

Resistance of a 1-inch cube, 13.98 microhms.

Approximate percentage resistance per degree C. (1.8 F. at 20 C. 88 F.) 0.389 per cent.

Elcctro-chemical equivalent (hydrogen = .0105) .2560 (See Thermo-Electric Series.)

Anvil. An intermittent contact, or "make and break" of the current is sometimes produced by directly pressing a key down upon a metallic surface, the two being terminals of the circuit. The surface or stud on which such pressure is produced is called the anvil. The ordinary telegraph key, which makes a contact by the pressure of the operator's fingers does it by making a contact between a contact piece upon the front end of the key and the anvil. In the induction coil the anvil is also found. Thus in the cut representing the end of an induction coil and its circuit breaker in which O and O' and P and P' represent the secondary circuit terminal connections A is the core of soft iron wires, h is the anvil; the hammer when resting upon it so as to be in contact closes the circuit. When the current coming from the primary to the post i, passes through the hammer and anvil h, and emerges by m, it magnetizes the core; this attracts the hammer, which is made of or is armed with a mass of iron. This breaks the circuit. The hammer falls at once on the anvil, again making the circuit, and the action is repeated with great rapidity. Hammer and anvil or key and anvil connections should be made of platinum.



A. O. C. Abbreviation for Anodic Opening Contraction, q. v.

Aperiodic. adj. In an oscillating apparatus, or in the oscillating member of apparatus, the fact of having no reference to time of vibration; dead-beat.

Synonym. Dead-beat.


Fig. 18. ARAGO'S DISC.

Arago's Disc. An apparatus consisting of a disc of copper mounted horizontally, or on a vertical spindle, and so arranged as to be susceptible of rapid rotation. Immediately over it, and best with a pane of glass intervening, a magnetic needle is mounted on a pivot directly over the axis of the disc. If the disc is rotated the lines of force of the magnet are cut by it, and consequently currents are produced in the copper. These currents act upon the needle and cause it to rotate, although quite disconnected. It is advisable for the needle to be strong and close to the disc, which should rotate rapidly.

Arc v. To form a voltaic arc.

Arc, Compound. A voltaic arc springing across between more than two electrodes.

Arc, Metallic. The voltaic arc produced between terminals or electrodes of metal. The characteristics of such arc as contrasted with the more usual arc between carbon electrodes are its greater length for the same expenditure of energy, its flaming character and characteristic colors due to the metals employed. It is sometimes, for the latter reason, used in spectroscopic investigations.

Arc Micrometer. A micrometer for measuring the distance between the electrodes of a voltaic arc.

Arc, Simple. A voltaic arc produced, as usual, between only two electrodes.


Arc, Voltaic. The voltaic arc is the arc between two carbon electrodes slightly separated, which is produced by a current of sufficient strength and involving sufficient potential difference. The pencils of carbon are made terminals in a circuit. They are first placed in contact and after the current is established they are separated a little. The current now seems to jump across the interval in what sometimes appears an arch of light. At the same time the carbon ends become incandescent. As regards the distance of separation with a strong current and high electro-motive force, the arc may be several inches long.

The voltaic arc is the source of the most intense heat and brightest light producible by man. The light is due principally to the incandescence of the ends of the carbon pencils. These are differently affected. The positive carbon wears away and becomes roughly cupped or hollowed; the negative also wears away, but in some cases seems to have additions made to it by carbon from the positive pole. All this is best seen when the rods are slender compared to the length of the arc.

It is undoubtedly the transferred carbon dust which has much to do with its formation. The conductivity of the intervening air is due partly, perhaps, to this, but undoubtedly in great measure to the intense heating to which it is subject. But the coefficient of resistance of the intervening air is so much higher than that of any other part of the circuit that an intense localization of resistance occurs with corresponding localization of heating effect. This is the cause of the intense light. Thus if the carbons are but 1/32 of an inch apart as in a commercial lamp the resistance may be 1.5 ohms. The poor thermal conductivity of the carbon favors the concentration of heat also. The apparent resistance is too great to be accounted for by the ohmic resistance of the interposed air. A kind of thermoelectric effect is produced. The positive carbon has a temperature of about 4,000 C. (7,232 F.), the negative from 3,000 C. (5,432 F.) to 3,500 C. (6,322 F.). This difference of temperature produces a counter-electro-motive force which acts to virtually increase the resistance of the arc. The carbon ends of an arc can be projected with the lantern. Globules are seen upon them due to melted silica from the arc of the carbon.



Areometer. An instrument for determining the specific gravity of a fluid. It consists of an elongated body ballasted so as to float vertically and provided with a mark or a scale. It floats deeper in a light than in a heavy liquid. If it carries but one mark weights are added until that mark is reached, when the weights required give the specific gravity. Or the scale may give the reading directly based upon the depth to which it sinks. Areometers are often made of glass, ballasted with shot or mercury enclosed in their bottom bulb as shown. They are used in regulating battery solutions, and in watching the charging and discharging of storage batteries.



Areometer, Bead. A tube of glass containing beads of different specific gravities. It has apertures at top and bottom. When immersed in a liquid, the same fills it, and the specific gravity within certain limits, depending on the factors of the beads, is shown by the beads which float and those which sink. It is used for storage batteries and other purposes where acids and solutions have to be tested.

Argyrometry. The method of ascertaining the weight and inferentially the thickness of an electroplater's deposit of silver. It is done by weighing the article before and after plating.

Arm. The four members of a Wheatstone bridge, q. v., are termed its arms. Referring to the diagram of a bridge, P, Q, R, S, are the arms.


Armature. (a.) A mass or piece of iron or steel, or a collection of pieces of iron designed to be acted on by a magnet. While nickel or cobalt might be used, they rarely or never are except in experimental apparatus. The armature of a permanent horse shoe magnet is simply a little bar of soft iron. When the magnet is not in use it is kept in contact with the poles with the idea of retaining its magnetism. It is then said to be used as a keeper. A bar magnet does not generally have an armature. The armature is also used to exhibit the attraction of the magnet.

Sometimes an armature is made of steel and is permanently magnetized. Such an armature, termed a polarized armature, is repelled when its like poles are opposed to like poles of the magnet and otherwise is attracted with force due to the sums of the magnetism. If the magnet is sufficiently powerful depolarization of the armature may ensue when like poles are opposed to like poles. Polarized armatures are used in various appliances, magneto generators, telegraphic instruments and others.

(b) In a dynamo or Motor the mass of laminated iron or of wire which carries the coils of insulated wires which are caused to rotate in the field of force of the field magnets in order to establish and maintain potential difference with its accompanying current, or which rotates under the effects of a current in a motor. (See Dynamo Electric Generator.)

The work of the armature core is twofold. It acts as a portion of the magnetic circuit, conducting the lines of force, and by virtue of its high permeability or multiplying power concentrating a number of the lines of force through its own substance. To enable it to act with efficiency in this direction it should be made of iron of the highest permeability, and should approach as closely as possible to the armature cores consistent with leaving space for the wire winding. It next acts as a support for the wires which are to be swept through the field of force. Thus it acts both to establish a strong field and then acts as a carrier for the wires which are to be cut by the wires in question. In connection with this subject the different definitions under Armature, Dynamo, Commutator, Induction and similar topics may be consulted.

(c) See Armature of Influence Machine.

(d) See Armature of Leyden Jar or Static Condenser.


Armature, Bar. An armature in a dynamo or motor whose winding is made up of conductors in the form of bars, round, rectangular and of other sections. This type of armature conductor is objectionable as Foucault currents are produced in it. It is found best to laminate or subdivide low resistance armature windings.

[Transcriber's Note: Foucault currents are also called eddy currents.]

Armature, Bipolar. An armature in which two poles are induced by the field. A bipolar field magnet produces a bipolar armature.

Armature Bore. The cylindrical space defined by the pole pieces of a dynamo or motor within which the armature rotates.

Synonym—Armature Chamber.


Armature, Closed Coil. An armature for a motor or dynamo, the ends of all of whose coils are united, so as to be in one closed circuit all the way around.


Armature Coil, or Coils. The insulated wire wound around the core of the armature of an electric current generator or motor.

Armature Core. The central mass of iron on which the insulated wire, to be rotated in the field of an electric current generator or motor, is wound. (See Dynamo-electric Machine and Motor, Electric.)

Armature, Cylinder. An armature of the Gramme ring type, but longer in the axial direction, so that its core resembles a long hollow cylinder, the wire being wound inside and outside as in the Gramme ring. (See Gramme Ring.)

Armature, Disc. (a) An armature of a dynamo electric machine or motor in which the coils are wound so as to be flat and are carried on the face of a disc forming the core or part of the core of the armature. S. P. Thompson treats it as a modified drum armature extended radially, the outer periphery corresponding to the back end of the drum. The poles of the field are generally placed to face the side or sides of the disc.

(b) Another type of disc armature has its wire wound on bobbins arranged around the periphery of a disc.

In disc armatures there is often no iron core, their thinness enabling this to be dispensed with.




Armature, Discoidal Ring. In a dynamo an armature of the shape of a ring of considerable radial depth of section as compared to its axial depth. It is generally made of iron ribbon or thin band wound to the proper size.

Synonym—Flat Ring Armature.


Armature, Drum. An armature for a dynamo or motor, consisting of a cylinder of iron preferably made up of discs insulated from each other by thin shellacked paper, or simply by their oxidized surfaces, and wound with wire parallel to the axis where it lies on the cylindrical periphery and crossing the heads approximately parallel to the diameter. It operates practically on the same principle as a Gramme Ring Armature. (See Gramme Ring.)

Synonym—Cylindrical Armature.

Armature Factor. The number of conductors on an armature, counted or enumerated all around its external periphery.

Armature, Hinged. An armature pivoted to the end of one of the legs of an electro-magnet so as to be free to swing and bring its other end down upon the other pole.


Armature, Hole. An armature whose core is perforated to secure cooling.

Synonym—perforated Armature.

Armature, Intensity. An armature wound for high electro-motive force. A term little used at the present time.

Armature Interference. A limit to the ampere turns permissible on a given armature is found in the increase of cross magnetizing effect, q. v., the increased lead necessitated, and the growth of the demagnetizing power. All such perturbing effects are sometimes expressed as armature interference.


Armature, Load of. The circumflux, q. v., of the armature, or the ampere turns of the same. The maximum load which can be carried by an armature without sparking is directly proportional to the radial depth of core and to the length of the gap, and inversely proportional to the breadth of the polar span.

Armature, Multipolar. An armature in which a number of poles greater than two is determined by the field. A multipolar field is employed for its production.

Armature, Neutral. An armature of a magnet or telegraph relay which is not polarized or magnetized.

Synonym—Non-polarized Armature—Neutral Relay Armature.

Armature of Influence Machine. Pieces of paper pasted on the stationary plate of an electric machine of the Holtz type.

Armature of Leyden Jar or Static Condenser. The inner and outer tin-foil coatings of a Leyden jar or other condenser.

Armature, Open Coil. An armature of a dynamo or motor on which the coils are not joined in one closed circuit, but have their ends or some of them separated, and connected each to its own commutator bar or each set to their own bar.



Armature, Pivoted. An armature for an electro-magnet mounted on a pivot, which is at right angles to the yoke or parallel with the legs of the magnet, so as to be free to rotate. When the magnet is excited the armature is drawn into line or approximately so with its base or yoke. The system is used in some telegraph apparatus.

Armature Pockets. Spaces or recesses in armatures provided for the reception of the coils.

Armature, Polarized. An armature made of steel or having a steel core to which permanent magnetism has been imparted. Such are used in some forms of magneto current generators, and in telegraphic instruments. (See Relay, Polarized.)

Armature, Pole. An armature having coils wound on separate poles projecting radially all around the periphery of its central hub or disc, or projecting internally from a ring-like frame, their ends facing the field magnet.

Synonym—Radial Armature.

Armature, Quantity. An armature of a dynamo or motor wound for current of large quantity. The term is now but little used.

Armature-Reactions. When an armature is running in an active dynamo a series of reactions is established, the more important of which are: I. A tendency to cross-magnetize the armature. II. A tendency to spark at the brushes. III. A tendency for the armature current to demagnetize on account of the lead which has to be given to the brushes. IV. Variations in the neutral points as more or less current is taken from the machine. V. Heating of armature, both core and conductors, and of pole pieces, which heating is due to Foucault currents.

Armature, Revolving, Page's. An early form of motor. The field is produced by a permanent magnet. Above its poles is a soft iron armature wound with a coil of insulated wire. A two-part commutator with contact springs conveys the current to the coil. The whole is so arranged that the polarity of the armature, as induced by the coil, through which a current is passed, is reversed as its ends sweep by the poles of the magnet. Then it is repelled from the poles and swings through 180 to have its polarity reversed and to go through the next 180, and so on. Thus it rotates at a very high rate of speed.

In the cut showing the elevation A, B, is the armature; f, g, the springs or brushes; h, the commutator with its sections o, i. In the section of the commutator W, W, designate the springs or brushes, A, the vertical spindle carrying the armature and commutator, and S, S, the commutator sections.



Fig. 29. SECTION OF COMMUTATOR OF PAGE'S REVOLVING ARMATURE. W, W, Brushes; A, Spindle; S, S, Armature Segments.

Armature, Ring. An armature whose core is in the shape of a ring, as the Gramme Ring Armature. (See Figs. 23 & 27.)


Armature, Rolling. (a) An armature for a permanent horseshoe magnet consisting of a straight cylinder of soft iron on which a heavy wheel is mounted. When the legs of the magnet are inclined downward and the bar is laid across them it rolls down to the poles, across their ends, and back up the under side. It is merely a magnetic toy or illustrative experiment.

Synonym—Wheel Armature.

(b) Another form consists of little bars of iron with brass discs attached to the ends. On placing two of these together and bringing the poles of a magnet near them, as shown, they become magnetized with like polarity by induction and repel each other, rolling away in opposite directions.



Armature, Shuttle. The original Siemens' armature, now discarded. The core was long and narrow, and its cross section was nearly of the section of an H. The grooves were wound full of wire, so that the whole formed almost a perfect cylinder, long and narrow comparatively. (See Winding Shuttle.)

Synonym—Siemens' Old Armature—Girder Armature—H Armature.


Armature, Spherical. An armature of a dynamo which is wound on a spherical core, so as to be almost a sphere. It is employed in the Thomson-Houston dynamo, being enclosed in a cavity nearly fitting it, formed by the pole pieces.

Armature, Stranded Conductor. A substitute for bar-armatures in which stranded copper wire conductors are substituted for the solid bar conductors, to avoid Foucault currents. (See Armature, Bar.)


Armature, Unipolar. An armature of a unipolar dynamo. (See Dynamo Unipolar.)

Armor of Cable. The metal covering, often of heavy wire, surrounding a telegraph or electric cable subjected to severe usage, as in submarine cables.

Synonym—Armature of Cable.

Arm, Rocker. An arm extending from a rocker of a dynamo or motor, to which arm one of the brushes is attached. (See Rocker.) Ordinarily there are two arms, one for each brush.

Articulate Speech. Speech involving the sounds of words. It is a definition which has acquired importance in the Bell telephone litigations, one contention, concerning the Bell telephone patent, holding that the patentee did not intend his telephone to transmit articulations, but only sound and music.

Astatic. adj. Having no magnetic directive tendency due to the earth's magnetism. Examples are given under Astatic Needle; Circuit, Astatic; and Galvanometer Astatic.



Astatic Needle. A combination of two magnetic needles so adjusted as to have as slight directive tendency as possible. Such a pair of needles when poised or suspended will hardly tend to turn more to one point of the compass than another. The combination is generally made up of two needles arranged one above the other, with their poles in opposite directions. This combination is usually called Nobili's pair. If of equal strength and with parallel magnetic axes of equal length they would be astatic. In practice this is very rarely the case. A resultant axis is generally to be found which may even be at right angles to the long axis of the magnets, causing them to point east and west. Such a compound needle requires very little force to turn it one way or the other. If one of the needles is placed within a coil of insulated wire a feeble current will act almost as strongly to deflect the system as if the other was absent, and the deflection will only be resisted by the slight directive tendency of the pair of needles. This is the basis of construction of the astatic galvanometer. Sometimes coils wound in opposite directions and connected in series, or one following the other, surround both needles, thus producing a still greater effect of deflection.

Other astatic needles are shown in the cuts below. [Figures 33 to 35.]



Asymptote. A line continuously approached by a curve, but which the curve, owing to its construction or nature of curvature, can never touch, be tangent to, or intersect.

Atmosphere. (a) A term applied to the atmospheric pressure as a practical unit of pressure equal to 15 lbs. to the square inch as generally taken. It is really about 14.7 lbs. per square inch, or 1,033 grams per square centimeter.

(b) Air, q. v.

Atmosphere Residual. The atmosphere left in a vessel after exhaustion. The term may be applied to any gas. In an incandescent lamp after flashing the residual atmosphere consists of hydro-carbons.

Atmospheric Electricity. The electricity of the atmosphere, rarely absent, but often changing in amount and sign. Benjamin Franklin, in a memoir published in 1749, indicated the method of drawing electricity from the clouds by pointed conductors. In June, 1752, he flew a kite and by its moistened cord drew an electric spark from the clouds, confirming his hypothesis that lightning was identical with the disruptive discharge of electricity. To observe electricity in fine weather a gold-leaf or other electroscope may be connected to the end of a long pointed insulated conductor. The electricity during thunderstorms can be shown by a similar arrangement, or burning alcohol or tinder gives an ascending current of warm air that acts as a conductor. Quite elaborate apparatus for observing and recording it have been devised. Atmospheric electricity is usually positive, but occasionally negative. When the sky is cloudless it is always positive, increasing with the elevation and isolation of the place. In houses, streets, and under trees no positive electricity can be found. In the Isle of Arran, Scotland, a rise of 24 to 48 volts per foot of increase in elevation was found by Sir William Thomson. At sunrise the electrification of the air is feeble, it increases towards noon and decreases again to reach a second maximum a few hours after sunset. It increases with the barometric pressure generally. In cloudy weather it is sometimes negative and the sign often changes several times in the same day. In a thunderstorm the changes in sign and potential are very rapid. The cause of atmospheric electricity is far from clear. Tait attributes it to a contact effect between air and water vapor, Solmeke to friction of water vesicles against ice particles in the upper atmosphere, he first showing that the two may coexist. The cause of the enormous increase of potential producing lightning is attributed to the decreased capacity due to the change of water from cloud vesicles to drops, thus diminishing the electrostatic capacity of the water in question. (See Lightning.)


Atom. The ultimate particle or division of an elementary substance; the smallest part that can exist in combination, and one which cannot exist alone. An elementary substance is composed of molecules just as truly as a compound one, but the atoms in the molecule of an elementary substance are all precisely alike. Hence atoms are the units of chemistry, they have to do with combinations, but the physical unit, the smallest particle of matter that can have an independent existence, is the molecule. The two are often confounded, especially by writers of a few years ago, so that by "atom" the molecule is often meant. There is nothing to be said of their size or mass. All such calculations refer to the molecule, q. v., often spoken of and called the atom.

[Transcriber's note: Yet to be discovered: electron—1897 (5 years), proton—1920 (28 years), neutron—1932 (30 years), quark—1961 (69 years).]

Atomic Attraction. The attraction of atoms for each other, in virtue of which they combine into molecules; chemical affinity, q. v., treats principally of this, although molecular attraction also plays a part in it.

Atomic Heat. The product of the atomic weight of a substance by its specific heat. This product is approximately the same, 6.4; this approximation is so close that it is of use in determining the valency and atomic weights of substances. The atomic weight of a substance therefore represents the approximate number of gram-calories required to raise one gram-atom, q. v., of such substance through 1 C. (1.8 F.)

Atomicity. The quantivalence or valency of the atoms; the number of combination bonds, or bonds of affinity, possessed by the atoms of any substance. Thus two atoms of hydrogen combine with one atom of oxygen, and three of oxygen with one of sulphur, forming saturated compounds. Therefore, taking hydrogen as of single atomicity or a monad, oxygen is of double atomicity or a dyad, and sulphur is of six-fold atomicity, or a hexad. The elements are thus classified into seven orders of atomicities, thus:

1, Monads or Univalent elements, Hydrogen, etc. 2, Dyads or Bivalent " Oxygen, etc. 3, Triads or Trivalent " Nitrogen, etc. 4, Tetrads or Quadrivalent " Lead, etc. 5, Pentads or Quinquivalent " Phosphorous, etc. 6, Hexads or Sexivalent " Chromium, etc. 7, Heptads or Septivalent " Chromium, etc.

The same element often possesses several atomicities. Barium is generally a dyad, sometimes a tetrad; nitrogen acts as a monad, dyad, triad, tetrad and pentad. The familiar electrolysis of water, giving two volumes of hydrogen to one of oxygen, is one of the illustrations of the theory indicating that two atoms of hydrogen are combined with one of oxygen.


Atomic Weight. The number expressing the relative weight of the atom of any substance, that of hydrogen being generally taken as unity. This is the universal system, although any other element might be taken as the basis of the system. The whole theory of atomic weights is based on the indivisibility of the atom and on the theory of atomicity, q. v. (See Equivalents.)

[Transcriber's note: The standard is now the isotope carbon-12 as exactly 12.]

Attraction. The tendency to approach and adhere or cohere, shown by all forms of matter. It includes gravitation, cohesion, adhesion, chemical affinity and other forms, and is opposed by repulsion, and is sometimes overcome by it, although it may be assumed to be always present. See the different kinds of attractions under their titles: Atomic Attraction, Electro-magnetic Attraction and Repulsion, Electro Static Attraction and Repulsion, Electro-dynamic Attraction and Repulsion; Magnetic Attraction and Repulsion; Molar Attraction.

Audiometer. An apparatus for obtaining a balance of induction from two coils acting upon a third. The third is placed between the other two and is free to move towards either. A scale is provided to show the extent of its movement. A varying or interrupted current being passed through the two outer coils, the preponderating current will produce the most induction if the central coil is equidistant. It can always be moved to such a point that there will be no inductive effect, one counteracting the other. Thus its position measures the relative induction. A telephone is in circuit with the intermediate coil and is used to determine when its position is such that no current is induced in it. It is sometimes used as a direct test of hearing. (See Hughes' Induction Balance.)


Aura, Electrical. The blast of air produced at highly electrified points.

Aurora. A luminous display seen in the northern heavens in the northern hemisphere, where it is the Aurora Borealis, and seen in the southern heavens in the southern hemisphere, where it is called Aurora Australis, or indifferently for either, the Aurora Polaris. It takes the form of pale luminous bands, rays and curtains varying in color. Near the poles they are very numerous. A French commission observed 150 auroras in 200 days. Their height is variously estimated at from 90 to 460 miles; they are most frequent at the equinoxes and least so at the solstices. There is a secular variation also, they attain a maximum of occurrence every 11 years together with sun spots, with a minimum 5 or 6 years after the maximum. There is also a period of 60 years, coincident with disturbances in the earth's magnetism. Various attempts have been made to account for them. They have a constant direction of arc with reference to the magnetic meridian (q. v.) and act upon the magnetic needle; in high latitudes they affect telegraph circuits violently. There is a strong probability that they represent electric currents or discharges. De la Rive considers them due to electric discharges between the earth and atmosphere, which electricities are separated by the action of the sun in equatorial regions. According to Balfour Stewart, auroras and earth currents.(q. v.) may be regarded as secondary currents due to small but rapid changes in the earth's magnetism. The subject is very obscure. Stewart treats the earth as representing the magnetic core of an induction coil, the lower air is the dielectric, and the upper rarefied and therefore conducting atmosphere is the secondary coil. This makes the aurora a phenomenon of induced currents. Then the sun may be regarded as the instigator of the primary changes in the earth's lines of force representing the primary of an induction coil.

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