Chapter C: G. S (5)

Electro-magnet, Bar. A straight bar of iron surrounded with a magnetizing coil of wire. Bar electromagnets are not much used, the horseshoe type being by far the more usual.

Electro-magnet, Club-foot. An electro-magnet, one of whose legs only is wound with wire, the other being bare.

Fig. 148. CLUB-FOOT ELECTRO-MAGNETS WITH HINGED ARMATURES.

Electro-magnet, Hinged. An electro-magnet whose limbs are hinged at the yoke. On excitation by a current the poles tend to approach each other.

Fig. 149. ELECTRO-MAGNET, HINGED

Electro-magnetic Attraction and Repulsion. The attraction and repulsion due to electromagnetic lines of force, which lines always tend to take as short a course as possible and also seek the medium of the highest permeance. This causes them to concentrate in iron and steel or other paramagnetic substance and to draw them towards a magnet by shortening the lines of force connecting the two. It is exactly the same attraction as that of the permanent magnet for its armature, Ampére's theory bringing the latter under the same title. In the case of two magnets like poles repel and unlike attract. In the case of simple currents, those in the same direction attract and those in opposite directions repel each other. This refers to constant current reactions. Thus the attraction of unlike poles of two magnets is, by the Ampérian theory, the attraction of two sets of currents of similar direction, as is evident from the diagram. The repulsion of like poles is the repulsion of unlike currents and the same applies to solenoids, q. v. (See Magnetism and do. Ampére's Theory of--Induction, Electro-dynamic--Electro-magnetic Induction.)

218 STANDARD ELECTRICAL DICTIONARY.

Electro-magnetic Control. Control of a magnet, iron armature, or magnetic needle in a galvanometer, ammeter, voltmeter or similar instrument by an electro-magnetic field, the restitutive force being derived from an electro-magnet. The restitutive force is the force tending to bring the index to zero.

Electro-magnetic Field of Force. A field of electro-magnetic lines of force, q. v., established through the agency of an electric current. A wire carrying a current is surrounded by circular concentric lines of force which have the axis of the wire as the locus of their centres. Electro-magnets produce lines of force identical with those produced by permanent magnets. (See Field of Force--Magnetic Field of Force--Controlling Field--Deflecting Field.)

Electro-magnetic Induction. When two currents of unlike direction are brought towards each other, against their natural repulsive tendency work is done, and the consequent energy takes the form of a temporary increase in both currents. When withdrawn, in compliance with the natural tendency of repulsion, the currents are diminished in intensity, because energy is not expended on the withdrawal, but the withdrawal is at the expense of the energy of the system. The variations thus temporarily produced in the currents are examples of electro-magnetic induction. The currents have only the duration in each case of the motion of the circuits. One circuit is considered as carrying the inducer current and is termed the primary circuit and its current the primary current, the others are termed the secondary circuit and current respectively. We may assume a secondary circuit in which there is no current. It is probable that there is always an infinitely small current at least, in every closed circuit. Then an approach of the circuits will induce in the secondary an instantaneous current in the reverse direction. On separating the two circuits a temporary current in the same direction is produced in the secondary.

219 STANDARD ELECTRICAL DICTIONARY.

A current is surrounded by lines of force. The approach of two circuits, one active, involves a change in the lines of force about the secondary circuit. Lines of force and current are so intimately connected that a change in one compels a change in the other. Therefore the induced current in the secondary may be attributed to the change in the field of force in which it lies, a field maintained by the primary circuit and current. Any change in a field of force induces a current or change of current in any closed circuit in such field, lasting as long as the change is taking place. The new current will be of such direction as to oppose the change. (See Lenz's Law.)

The action as referred to lines of force may be figured as the cutting of such lines by the secondary circuit, and such cutting may be brought about by moving the secondary in the field. (See Lines of Force--Field of Force.) The cutting of 1E8 lines of force per second by a closed circuit induces an electro-motive force of one volt. (See Induction, Mutual, Coefficient of.)

Electro-magnet, Iron Clad. A magnet whose coil and core are encased in a iron jacket, generally connected to one end of the core. This gives at one end two poles, one tubular, the other solid, and concentric with each other. It is sometimes called a tubular magnet.

Electro-magnet, One Coil. An electro-magnet excited by one coil. In some dynamos the field magnets are of this construction, a single coil, situated about midway between the poles, producing the excitation.

Electro-magnetic Leakage. The leakage of lines of force in an electro-magnet; the same as magnetic leakage. (See Magnetic Leakage.)

Electro-magnetic Lines of Force. The lines of force produced in an electro-magnetic field. They are identical with Magnetic Lines of Force, q. v. (See also Field of Force-Line of Force.)

Electro-magnetic Stress. The stress in an electro-magnetic field of force, showing itself in the polarization of light passing through a transparent medium in such a field. (See Magnetic Rotary Polarization.)

Electro-magnetic Theory of Light. This theory is due to J. Clark Maxwell, and the recent Hertz experiments have gone far to prove it. It holds that the phenomena of light are due to ether waves, identical in general factors with those produced by electro-magnetic induction of alternating currents acting on the ether. In a non-conductor any disturbance sets an ether wave in motion owing to its restitutive force; electricity does not travel through such a medium, but can create ether waves in it. Therefore a non-conductor of electricity is permeable to waves of ether or should transmit light, or should be transparent. A conductor on the other hand transmits electrical disturbances because it has no restitutive force and cannot support an ether wave. Hence a conductor should not transmit light, or should be opaque. With few exceptions dielectrics or non-conductors are transparent, and conductors are opaque.

220 STANDARD ELECTRICAL DICTIONARY.

Again, the relation between the electrostatic and electro-magnet units of quantity is expressed by 1 : 30,000,000,000; the latter figure in centimeters gives approximately the velocity of light. The electro-magnetic unit depending on electricity in motion should have this precise relation if an electro-magnetic disturbance was propagated with the velocity of light. If an electrically charged body were whirled around a magnetic needle with the velocity of light, it should act in the same way as a current circulating around it. This effect to some extent has been shown experimentally by Rowland.

A consequence of these conclusions is (Maxwell) that the specific inductive capacity of a non-conductor or dielectric should be equal to the square of its index of refraction for waves of infinite length. This is true for some substances--sulphur, turpentine, petroleum and benzole. In others the specific inductive capacity is too high, e. g., vegetable and animal oils, glass, Iceland spar, fluor spar, and quartz.

Electro-magnetic Unit of Energy. A rate of transference of energy equal to ten meg-ergs per second.

Electro-magnetism. The branch of electrical science treating of the magnetic relations of a field of force produced by a current, of the reactions of electro-magnetic lines of force, of the electromagnetic field of force, of the susceptibility, permeability, and reluctance of diamagnetic and paramagnetic substances, and of electro-magnets in general.

Electro-magnet, Long Range. An electro-magnet so constructed with extended pole pieces or otherwise, as to attract its armature with reasonably constant force over a considerable distance. The coil and plunger, q. v., mechanisms illustrate one method of getting an extended range of action. When a true electro-magnet is used, one with an iron core, only a very limited range is attainable at the best. (See Electro-magnet, Stopped Coil--do. Plunger.)

Electro-magnet, Plunger. An electro-magnet with hollow coils, into which the armature enters as a plunger. To make it a true electro-magnet it must have either a yoke, incomplete core, or some polarized mass of iron.

Electro-magnet, Polarized. An electro-magnet consisting of a polarized or permanently magnetized core wound with magnetizing coils, or with such coils on soft iron cores mounted on its ends. The coils may be wound and connected so as to cooperate with or work against the permanent magnet on which it is mounted. In Hughes' magnet shown in the cut it is mounted in opposition, so that an exceedingly feeble current will act to displace the armature, a, which is pulled away from the magnet by a spring, s.

221 STANDARD ELECTRICAL DICTIONARY.

Fig. 150 HUGHES' POLARIZED ELECTRO-MAGNET

Electro-magnets, Interlocking. Electro-magnets so arranged that their armatures interlock. Thus two magnets, A A and B B, may be placed with their armatures, M and N, at right angles and both normally pulled away from the poles. When the armature M is attracted a catch on its end is retained by a hole in the end of the other armature N, and when the latter armature N is attracted by its magnet the armature M is released. In the mechanism shown in the cut the movements of the wheel R are controlled. Normally it is held motionless by the catch upon the bottom of the armature M, coming against the tooth projecting from its periphery. A momentary current through the coils of the magnet A A releases it, by attracting M, which is caught and retained by N, and leaves it free to rotate. A momentary current through the coils of the magnet B B again releases M, which drops down and engages the tooth upon R and arrests its motion.

Fig. 151. INTERLOCKING ELECTRO-MAGNETS.

222 STANDARD ELECTRICAL DICTIONARY.

Electro-magnet, Stopped Coil. An electro-magnet consisting of a tubular coil, in which a short fixed core is contained, stopping up the aperture to a certain distance, while the armature is a plunger entering the aperture. This gives a longer range of action than usual.

Electro-magnet, Surgical. An electro-magnet, generally of straight or bar form, fitted with different shaped pole pieces, used for the extraction of fragments of iron or steel from the eyes. Some very curious cases of successful operations on the eyes of workmen, into whose eyes fragments of steel or iron had penetrated, are on record.

Electro-medical Baths. A bath for the person provided with connections and electrodes for causing a current of electricity of any desired type to pass through the body of the bather. Like all electro-therapeutical treatment, it should be administered under the direction of a physician only.

Electro-metallurgy. (a) In the reduction of ores the electric current has been proposed but never extensively used, except in the reduction of aluminum and its alloys. (See Reduction of Ores, Electric.)

(b) Electro-plating and deposition of metal from solutions is another branch. (See Electroplating and Electrotyping.)

(c) The concentration of iron ores by magnetic attraction may come under this head. (See Magnetic Concentration of Ores.)

Electrometer. An instrument for use in the measurement of potential difference, by the attraction or repulsion of statically charged bodies. They are distinguished from galvanometers as the latter are really current measurers, even if wound for use as voltmeters, depending for their action upon the action of the current circulating in their coils.

Electrometer, Absolute. An electrometer designed to give directly the value of a charge in absolute units. In one form a plate, a b, of conducting surface is supported or poised horizontally below a second larger plate C, also of conducting surface. The poised plate is surrounded by a detached guard ring--an annular or perforated plate, r g r' g'--exactly level and even with it as regards the upper surface. The inner plate is carried by a delicate balance. In use it is connected to one of the conductors and the lower plate to earth or to the other. The attraction between them is determined by weighing. By calculation the results can be made absolute, as they depend on actual size of the plates and their distance, outside of the potential difference of which of course nothing can be said. If S is the area of the disc, d the distance of the plates, V-V1 the difference of their potential, which is to be measured, and F the force required to balance their attraction, we have:

F = ( ( V - V1 )^2 * S ) / ( 8 * PI * d^2 )

223 STANDARD ELECTRICAL DICTIONARY.

If V = 0 this reduces to

F = ( V^2 * S ) / ( 8 * PI * d^2 ) (2)
or
V = d * SquareRoot( (8 * PI * F ) / S ) (3)

As F is expressed as a weight, and S and a as measures of area and length, this gives a means of directly obtaining potential values in absolute measure. (See Idiostatic Method--Heterostatic Method.)

Synonyms--Attracted Disc Electrometer--Weight Electrometer.

Fig. 152. SECTION OF BASE OF PORTABLE ELECTROMETER.

In some forms the movable disc is above the other, and supported at the end of a balance beam. In others a spring support, arranged so as to enable the attraction to be determined in weight units, is adopted. The cuts, Figs. 152 and 154, show one of the latter type, the portable electrometer. The disc portion is contained within a cylindrical vessel.

Fig. 153. DIAGRAM ILLUSTRATING THEORY OF ABSOLUTE ELECTROMETER.

Referring to Fig. 152 g is the stationary disc, charged through the wire connection r; f is the movable disc, carried by a balance beam poised at i on a horizontal and transverse stretched platinum wire, acting as a torsional spring. The position of the end k of the balance beam shows when the disc f is in the plane of the guard ring h h. The end k is forked horizontally and a horizontal sighting wire or hair is fastened across the opening of the fork. When the hair is midway between two dots on a vertical scale the lever is in the sighted position, as it is called, and the disc is in the plane of the guard ring.

224 STANDARD ELECTRICAL DICTIONARY.

Fig. 154. PORTABLE ELECTROMETER.

The general construction is seen in Fig. 154. There the fixed disc D is carried by insulating stem g1. The charging electrode is supported by an insulating stem g2, and without contact with the box passes out of its cover through a guard tube E, with cover, sometimes called umbrella, V. The umbrella is to protect the apparatus from air currents. At m is the sighting lens. H is a lead box packed with pumice stone, moistened with oil of vitriol or concentrated sulphuric acid, to preserve the atmosphere dry. Before use the acid is boiled with some ammonium sulphate to expel any corrosive nitrogen oxides, which might corrode the brass.

In use the upper disc is charged by its insulated electrode within the tube E; the movable disc is charged if desired directly through the case of the instrument. The upper disc is screwed up or down by the micrometer head M, until the sighted position is reached. The readings of the micrometer on the top of the case give the data for calculation.

225 STANDARD ELECTRICAL DICTIONARY.

Fig. 155. LIPPMAN'S CAPILLARY ELECTROMETER.

Electrometer, Capillary. An electrometer for measuring potential difference by capillary action, which latter is affected by electrostatic excitement. A tube A contains mercury; its end drawn out to a fine aperture dips into a vessel B which contains dilute sulphuric acid with mercury under it, as shown. Wires running from the binding-posts a and b connect one with the mercury in A, the other with that in B. The upper end of the tube A connects with a thick rubber mercury reservoir T, and manometer H. The surface tension of the mercury-acid film at the lower end of the tube A keeps all in equilibrium. If now a potential difference is established between a and b, as by connecting a battery thereto, the surface tension is increased and the mercury rises in the tube B. By screwing down the compressing clamp E, the mercury is brought back to its original position. The microscope M is used to determine this position with accuracy. The change in reading of the manometer gives the relation of change of surface tension and therefore of potential. Each electrometer needs special graduation or calibration, but is exceedingly sensitive and accurate. It cannot be used for greater potential differences than .6 volt, but can measure .0006 volt. Its electrostatic capacity is so small that it can indicate rapid changes. Another form indicates potential difference by the movement of a drop of sulphuric acid in a horizontal glass tube, otherwise filled with mercury, and whose ends lead into two mercury cups or reservoirs. The pair of electrodes to be tested are connected to the mercury vessels. The drop moves towards the negative pole, and its movement for small potential differences (less than one volt) is proportional to the electro-motive force or potential difference.

226 STANDARD ELECTRICAL DICTIONARY.

Electrometer Gauge. An absolute electrometer (see Electrometer, Absolute) forming an attachment to a Thomson quadrant electrometer. It is used to test the potential of the flat needle connected with the inner surface of the Leyden jar condenser of the apparatus. This it does by measuring the attraction between itself and an attracting disc, the latter connected by a conductor with the interior of the jar.

Electrometer, Lane's. A Leyden jar with mounted discharger, so that when charged to a certain point it discharges itself. It is connected with one coating of any jar whose charge is to be measured, which jar is then charged by the other coating. As the jar under trial becomes charged to a certain point the electrometer jar discharges itself, and the number of discharges is the measure of the charge of the other jar. It is really a unit jar, q. v.

Fig. 156. THOMSON'S QUADRANT ELECTROMETER.

Fig. 157. HENLEY'S QUADRANT ELECTROSCOPE.

227 STANDARD ELECTRICAL DICTIONARY.

Electrometer, Quadrant. (a) Sir William Thomson's electrometer, a simple form of which is shown in the cut, consists of four quadrants of metal placed horizontally; above these a broad flat aluminum needle hangs by a very fine wire, acting as torsional suspension. The quadrants are insulated from each other, but the opposite ones connect with each other by wires. The apparatus is adjusted so that, when the quadrants are in an unexcited condition the needle is at rest over one of the diametrical divisions between quadrants. The needle by its suspension wire is in communication with the interior of a Leyden jar which is charged. The whole is covered with a glass shade, and the air within is kept dry by a dish of concentrated sulphuric acid so that the jar retains its charge for a long time and keeps the needle at approximately a constant potential. If now two pairs of quadrants are excited with opposite electricities, as when connected with the opposite poles of an insulated galvanic cell, the needle is repelled by one pair and attracted by the other, and therefore rotates through an arc of greater or less extent. A small concave mirror is attached above the needle and its image is reflected on a graduated screen. This makes the smallest movement visible. Sometimes the quadrants are double, forming almost a complete box, within which the needle moves.

(b) Henley's quadrant electrometer is for use on the prime conductor of an electric machine, for roughly indicating the relative potential thereof. It consists of a wooden standard attached perpendicularly to the conductor. Near one end is attached a semi-circular or quadrant arc of a circle graduated into degrees or angular divisions. An index, consisting of a straw with a pith-bell attached to its end hangs from the center of curvature of the arc. When the prime conductor is charged the index moves up over the scale and its extent of motion indicates the potential relatively.

When the "quadrant electrometer" is spoken of it may always be assumed that Sir William Thomson's instrument is alluded to. Henley's instrument is properly termed a quadrant electroscope. (See Electroscope.)

Electro-motive Force. The cause which produces currents of electricity. In general it can be expressed in difference of potentials, although the term electro-motive force should be restricted to potential difference causing a current. It is often a sustained charging of the generator terminals whence the current is taken. Its dimensions are

(work done/the quantity of electricity involved),

or ( M * (L^2) /(T^2 ) ) / ((M^.5) * (L^.5)) = ( (M^.5) * (L^1.5) ) /(T^2)

The practical unit of electro-motive force is the volt, q. v. It is often expressed in abbreviated form, as E. M. D. P., or simply as D. P., i. e., potential difference.

Electro-motive force and potential difference are in many cases virtually identical, and distinctions drawn between them vary with different authors. If we consider a closed electric circuit carrying a current, a definite electro-motive force determined by Ohm's law from the resistance and current obtains in it. But if we attempt to define potential difference as proper to the circuit we may quite fail. Potential difference in a circuit is the difference in potential between defined points of such circuit. But no points in a closed circuit can be found which differ in potential by an amount equal to the entire electro-motive force of the circuit. Potential difference is properly the measure of electro-motive force expended on the portion of a circuit between any given points. Electro-motive force of an entire circuit, as it is measured, as it were, between two consecutive points but around the long portion of the circuit, is not conceivable as merely potential difference. Taking the circle divided in to degrees as an analogy, the electro-motive force of the entire circuit might be expressed as 360º, which are the degrees intervening between two consecutive points, measured the long way around the circle. But the potential difference between the same two points would be only 1º, for it would be measured by the nearest path.

[Transcriber's notes: If 360º is the "long" way, 0º is the "short". A formal restatement of the above definition of EMF: "If a charge Q passes through a device and gains energy U, the net EMF for that device is the energy gained per unit charge, or U/Q. The unit of EMF is a volt, or newton-meter per coulomb."]

228 STANDARD ELECTRICAL DICTIONARY.

Electro-motive Force, Counter. A current going through a circuit often has not only true or ohmic resistance to overcome, but meets an opposing E. M. F. This is termed counter-electro-motive force. It is often treated in calculations as resistance, and is termed spurious resistance. It may be a part of the impedance of a circuit.

In a primary battery hydrogen accumulating on the negative plate develops counter E. M. F. In the voltaic arc the differential heating of the two carbons does the same. The storage battery is changed by a current passing in the opposite direction to its own natural current; the polarity of such a battery is counter E. M. F.

Electro-motive Force, Unit. Unit electro-motive force is that which is created in a conductor moving through a magnetic field at such a rate as to cut one unit line of force per second. It is that which must be maintained in a circuit of unit resistance to maintain a current of unit quantity therein. It is that which must be maintained between the ends of a conductor in order that unit current may do unit work in a second.

Electro-motive Intensity. The force acting upon a unit charge of electricity. The mean force is equal to the difference of potential between two points within the field situated one centimeter apart, such distance being measured along the lines of force. The term is due to J. Clerk Maxwell.

Electro-motive Series. Arrangement of the metals and carbon in series with the most electro-positive at one end, and electronegative at the other end. The following are examples for different exciting liquids:

Dilute Sulphuric Dilute Hydrochloric Caustic Potassium Acid Acid. Potash. Sulphide.

Zinc Zinc Zinc Zinc Cadmium Cadmium Tin Copper Tin Tin Cadmium Cadmium Lead Lead Antimony Tin Iron Iron Lead Silver Nickel Copper Bismuth Antimony Bismuth Bismuth Iron Lead Antimony Nickel Copper Bismuth Copper Silver Nickel Nickel Silver Antimony Silver Iron Gold Platinum Carbon

In each series the upper metal is the positive, dissolved or attacked element.

229 STANDARD ELECTRICAL DICTIONARY.

Electro-motograph. An invention of Thomas A. Edison. A cylinder of chalk, moistened with solution of caustic soda, is mounted so as to be rotated by a handle. A diaphragm has an arm connected to its center. This arm is pressed against the surface of the cylinder by a spring. When the cylinder is rotated, a constant tension is exerted on the diaphragm. If a current is passed through the junction of arm and cylinder the electrolytic action alters the friction so as to change the stress upon the diaphragm.

If the current producing this effect is of the type produced by the human voice through a microphone the successive variations in strain upon the diaphragm will cause it to emit articulate sounds. These are produced directly by the movement of the cylinder, the electrolytic action being rather the regulating portion of the operation. Hence very loud sounds can be produced by it. This has given it the name of the loud- speaking telephone.

The same principle may be applied in other ways. But the practical application of the motograph is in the telephone described.

Fig. 158. ELECTRO-MOTOGRAPH TELEPHONE

Electro-motor. This term is sometimes applied to a current generator, such as a voltaic battery.

Electro-muscular Excitation. A term in medical electricity indicating the excitation of muscle as the effect of electric currents of any kind.

Electro-negative. adj. Appertaining to negative electrification; thus of the elements oxygen is the most electro-negative, because if separated by electrolytic action from any combination, it will be charged with negative electricity.

230 STANDARD ELECTRICAL DICTIONARY.

Electro-optics. The branch of natural science treating of the relations between light and electricity. Both are supposed to be phenomena of or due to the luminiferous ether. To it may be referred the following:

(a) Electro-magnetic Stress and Magnetic Rotary Polarization;

(b) Dielectric Strain; all of which may be referred to in this book;

(c) Change in the resistance of a conductor by changes in light to which it is exposed (see Selenium);

(d) The relation of the index of refraction of a dielectric to the dielectric constant (see Electro-magnetic Theory of Light);

(e) The identity (approximate) of the velocity of light in centimeters and the relative values of the electrostatic and electro-magnet units of intensity, the latter being 30,000,000,000 times greater than the former, while the velocity of light is 30,000,000,000 centimeters per second.

Electrophoric Action. The action of an electrophorous; utilized in influence machines. (See Electrophorous.)

Fig. 159. ELECTROPHOROUS.

Electrophorous. An apparatus for the production of electric charges of high potential by electrostatic induction, q. v. It consists of a disc of insulating material B, such as resin or gutta percha, which is held in a shallow metal-lined box or form. The disc may be half an inch thick and a foot or more in diameter, or may be much smaller and thinner. A metal disc A, smaller in diameter is provided with an insulating handle which may be of glass, or simply silk suspension strings. To use it the disc B is excited by friction with a cat-skin or other suitable substance. The metallic disc is then placed on the cake of resin exactly in its centre, so that the latter disc or cake projects on all sides. Owing to roughness there is little real electric contact between the metal and dielectric. On touching the metal disc a quantity of negative electricity escapes to the earth. On raising it from the cake it comes off excited positively, and gives a spark and is discharged. It can be replaced, touched, removed and another spark can be taken from it, and so on as long as the cake stays charged.

The successive discharges represent electrical energy expended. This is derived from the muscular energy expended by the operator in separating the two discs when oppositely excited. As generally used it is therefore an apparatus for converting muscular or mechanical energy into electric energy.

231 STANDARD ELECTRICAL DICTIONARY.

Electro-physiology. The science of the electric phenomena of the animal system. It may also be extended to include plants. The great discovery of Galvani with the frog's body fell into this branch of science. The electric fishes, gymnotus, etc., present intense phenomena in the same.

Electroplating. The deposition by electrolysis of a coating of metal upon a conducting surface. The simplest system makes the object to be plated the negative electrode or plate in a galvanic couple. Thus a spoon or other object may be connected by a wire to a plate of zinc. A porous cup is placed inside a battery jar. The spoon is placed in the porous cup and the zinc outside it. A solution of copper sulphate is placed in the porous cup, and water with a little sodium or zinc sulphate dissolved in it, outside. A current starts through the couple, and copper is deposited on the spoon.

A less primitive way is to use a separate battery as the source of current; to connect to the positive plate by a wire the object to be plated, and a plate of copper, silver, nickel or other metal to the other pole of the battery. On immersing both object and plate (anode) in a bath of proper solution the object will become plated.

In general the anode is of the same material as the metal to be deposited, and dissolving keeps up the strength of the bath. There are a great many points of technicality involved which cannot be given here. The surface of the immersed object must be conductive. If not a fine wire network stretched over it will gradually fill up in the bath and give a matrix. More generally the surface is made conductive by being brushed over with plumbago. This may be followed by a dusting of iron dust, followed by immersion in solution ot copper sulphate. This has the effect of depositing metallic copper over the surface as a starter for the final coat.

Attention must be paid to the perfect cleanliness of the objects, to the condition of the bath, purity of anodes and current density.

Voltaic batteries are largely used for the current as well as special low resistance dynamos. Thermo-electric batteries are also used to some extent but not generally.

Electro-pneumatic Signals. Signals, such as railroad signals or semaphores, moved by compressed air, which is controlled by valves operated by electricity. The House telegraph, which was worked by air controlled by electricity, might come under this term, but it is always understood as applied to railroad signals, or their equivalent.

232 STANDARD ELECTRICAL DICTIONARY.

Electropoion Fluid. An acid depolarizing solution for use in zinc-carbon couples, such as the Grenet battery. The following are formulae for its preparation:

(a) Dissolve one pound of potassium bichromate in ten pounds of water, to which two and one-half pounds of concentrated sulphuric acid have been gradually added. The better way is to use powdered potassium bichromate, add it to the water first, and then gradually add the sulphuric acid with constant stirring.

(b) To three pints of water add five fluid ounces of concentrated sulphuric acid; add six ounces pulverized potassium bichromate.

(c) Mix one gallon concentrated sulphuric acid and three gallons of water. In a separate vessel dissolve six pounds potassium bichromate in two gallons of boiling water. Mix the two.

The last is the best formula. Always use electropoion fluid cold. (See Trouvé's Solution--Poggendorff's Solution--Kakogey's Solution-- Tissandrier's Solution--Chutaux's Solution.)

Electro-positive. adj. Appertaining to positive electrification; thus potassium is the most electro-positive of the elements. (See Electro-negative.)

Electro-puncture. The introduction into the system of a platinum point or needle, insulated with vulcanite, except near its point, and connected as the anode of a galvanic battery. The kathode is a metal one, covered with a wet sponge and applied on the surface near the place of puncture. It is used for treatment of aneurisms or diseased growths, and also for removal of hair by electrolysis. (See Hair, Removal of by Electrolysis.)

Synonym--Galvano-puncture.

Electro-receptive. adj. A term applied to any device or apparatus designed to receive and absorb electric energy. A motor is an example of an electro-receptive mechanism.

Electroscope. An apparatus for indicating the presence of an electric charge, and also for determining the sign, or whether the charge is positive or negative. The simplest form consists of a thread doubled at its centre and hung therefrom. On being charged, or on being connected to a charged body the threads diverge. A pair of pith balls may be suspended in a similar way, or a couple of strips of gold leaf within a flask (the gold leaf electroscope). To use an electroscope to determine the sign of the charge it is first slightly charged. The body to be tested is then applied to the point of suspension, or other charging point. If at once further repelled the charge of the body is of the same sign as the slight charge first imparted to the electroscope leaves; the leaves as they become more excited will at once diverge more. If of different sign they will at first approach as their charge is neutralized and will afterwards diverge.

The gold-leaf electroscope is generally enclosed in a glass bell jar or flask. Sometimes a pair of posts rise, one on each side, to supply points of induction from the earth to intensify the action. (See Electrometer, Quadrant--Electroscope, Gold leaf, and others.)

233 STANDARD ELECTRICAL DICTIONARY.

Electroscope, Bennett's. A gold-leaf electroscope, the suspended leaves of which are contained in a glass shade or vessel of dry air. On the inside of the glass shade are two strips of gold leaf, which rise from the lower edge a short distance, being pasted to the glass, and connected to the ground. These act by induction to increase the sensitiveness of the instruments.

Electroscope, Bohenberger's. A condensing electroscope (see Electroscope, Condensing) with a single strip of gold leaf suspended within the glass bell. This is at an equal distance from the opposite poles of two dry piles (see Zamboni's Dry Pile) standing on end, one on each side of it. As soon as the leaf is excited it moves toward one and away from the other pile, and the sign of its electrification is shown by the direction of its motion.

Electroscope, Condensing. A gold leaf electroscope, the glass bell of which is surmounted by an electrophorous or static condenser, to the lower plate of which the leaves of gold are suspended or connected.

In use the object to be tested is touched to the lower plate, and the upper plate at the same time is touched by the finger. The plates are now separated. This reduces the capacity of the lower plate greatly and its charge acquires sufficient potential to affect the leaves, although the simple touching may not have affected them at all.

Electroscope, Gold Leaf. An electroscope consisting of two leaves of gold leaf hung in contact with each other from the end of a conductor. When excited they diverge. The leaves are enclosed in a glass vessel.

Fig. 160. GOLD LEAF ELECTROSCOPE.

234 STANDARD ELECTRICAL DICTIONARY.

Electroscope, Pith Ball. Two pith balls suspended at opposite ends of a silk thread doubled in the middle. When charged with like electricity they repel each other. The extent of their repulsion indicates the potential of their charge.

Electrostatic Attraction and Repulsion. The attraction and repulsion of electrostatically charged bodies for each other, shown when charged with electricity. If charged with electricity of the same sign they repel each other. If with opposite they attract each other. The classic attraction and subsequent repulsion of bits of straw and chaff by the excited piece of amber is a case of electrostatic attraction and repulsion. (See Electricity, Static--Electrostatics--Coulomb's Laws of Electrostatic Attraction and Repulsion.)

Electrostatic Induction, Coefficient of. The coefficient expressing the ratio of the charge or change of charge developed in one body to the potential of the inducing body.

Electrostatic Lines of Force. Lines of force assumed to exist in an electrostatic field of force, and to constitute the same. In general they correspond in action and attributes with elcctro-magnetic lines of force. They involve in almost all cases either a continuous circuit, or a termination at both ends in oppositely charged surfaces.

Fig. 161. ELECTROSTATIC LINES OF FORCE BETWEEN NEAR SURFACES.

Fig. 162. ELECTROSTATIC LINKS OF FORCE BETWEEN DISTANT SURFACES.

235 STANDARD ELECTRICAL DICTIONARY.

The cut, Fig. 161, shows the general course taken by lines of force between two excited surfaces when near together. Here most of them are straight lines reaching straight across from surface to surface, while a few of them arch across from near the edges, tending to spread. If the bodies are drawn apart the spreading tendency increases and the condition of things shown in the next cut, Fig. 162, obtains. There is an axial line whose prolongations may be supposed to extend indefinitely, as occupying a position of unstable equilibrium. Here the existence of a straight and unterminated line of force may be assumed.

A direction is predicated to lines of force corresponding with the direction of an electric current. They are assumed to start from a positively charged and to go towards a negatively charged surface. A positively charged body placed in an electrostatic field of force will be repelled from the region of positive into or towards the region of negative potential following the direction of the lines of force, not moving transversely to them, and having no transverse component in its motion.

[Transcriber's note: More precisely, "A positively charged body placed in an electrostatic field of force will be repelled from the region of positive into or towards the region of negative potential ACCELERATING in the direction of the lines of force, not ACCELERATING transversely to them, and having no transverse component in its ACCELERATION." Previously acquired momentum can produce a transverse component of VELOCITY.]

Electrostatics. The division of electric science treating of the phenomena of electric charge, or of electricity in repose, as contrasted with electro-dynamics or electricity in motion or in current form. Charges of like sign repel, and of unlike sign attract each other. The general inductive action is explained by the use of the electrostatic field of force and electrostatic lines of force, q. v. The force of attraction and repulsion of small bodies or virtual points, which are near enough to each other, vary as the square of the distance nearly, and with the product of the quantities of the charges of the two bodies.

Electrostatic Refraction. Dr. Kerr found that certain dielectrics exposed to electric strain by being placed between two oppositely excited poles of a Holtz machine or other source of very high tension possess double refracting powers, in other words can rotate a beam of polarized light, or can develop two complimentary beams from common light. Bisulphide of carbon shows the phenomenon well, acting as glass would if the glass were stretched in the direction of the electrostatic lines of force. To try it with glass, holes are drilled in a plate and wires from an influence machine are inserted therein. The discharge being maintained through the glass it polarizes light.

Synonym--Kerr Effect.

Electrostatic Series. A table of substances arranged in the order in which they are electrostatically charged by contact, generally by rubbing against each other. The following series is due to Faraday. The first members become positively excited when rubbed with any of the following members, and vice versa. The first elements correspond to the carbon plate in a galvanic battery, the succeeding elements to the zinc plate.

Cat, and Bear-skin--Flannel--Ivory--Feathers--Rock Crystal--Flint Glass--Cotton--Linen--Canvas--White Silk--the Hand--Wood--Shellac--the Metals (Iron-Copper-Brass-Tin-Silver-Platinum)--Sulphur. There are some irregularities. A feather lightly drawn over canvas is negatively electrified; if drawn through folds pressed against it it is positively excited. Many other exceptions exist, so that the table is of little value.

236 STANDARD ELECTRICAL DICTIONARY.

Electrostatic Stress. The stress produced upon a transparent medium in an electrostatic field of force by which it acquires double refracting or polarizing properties as regards the action of such medium upon light. (See Electrostatic Refraction.)

Electro-therapeutics or Therapy. The science treating of the effects of electricity upon the animal system in the treatment and diagnosis of disease.

Electrotonus. An altered condition of functional activity occurring in a nerve subjected to the passage of an electric current. If the activity is decreased, which occurs near the anode, the state is one of anelectrotonus, if the activity is increased which occurs near the kathode the condition is one of kathelectrotonus.

Electrotype. The reproduction of a form of type or of an engraving or of the like by electroplating, for printing purposes. The form of type is pressed upon a surface of wax contained in a shallow box. The wax is mixed with plumbago, and if necessary some more is dusted and brushed over its surface and some iron dust is sprinkled over it also. A matrix or impression of the type is thus obtained, on which copper is deposited by electroplating, q. v.

Element, Chemical. The original forms of matter that cannot be separated into constituents by any known process. They are about seventy in number. Some of the rarer ones are being added to or cancelled with the progress of chemical discovery. For their electric relations see Electro-chemical Equivalents--Electro-chemical Series.

The elements in entering into combination satisfy chemical affinity and liberate energy, which may take the form of electric energy as in the galvanic battery, or of heat energy, as in the combustion of carbon or magnesium. Therefore an uncombined element is the seat of potential energy. (See Energy, Potential.) In combining the elements always combine in definite proportions. A series of numbers, one being proper to each element which denote the smallest common multipliers of these proportions, are called equivalents. Taking the theory of valency into consideration the product of the equivalents by the valencies gives the atomic weights.

237 STANDARD ELECTRICAL DICTIONARY.

Element, Mathematical. A very small part of anything, corresponding in a general way to a differential, as the element of a current.

Element of a Battery Cell. The plates in a galvanic couple are termed elements, as the carbon and zinc plates in a Bunsen cell. The plate unattacked by the solution, as the carbon plate in the above battery, is termed the negative plate or element; the one attacked, as the zinc plate, is termed the positive plate or element.

Synonym--Voltaic Element.

Elements, Electrical Classification of. This may refer to Electro-chemical Series, Electrostatic Series, or Thermo-electric Series, all of which may be referred to.

Element, Thermo-electric. One of the metals or other conductors making a thermo-electric couple, the heating of whose junction produces electro-motive force and a current, if on closed circuit. The elements of a couple are respectively positive and negative, and most conductors can be arranged in a series according to their relative polarity. (See Thermo-electric Series.)

Elongation. The throw of the magnetic needle. (See Throw.)

Synonym--Throw.

Embosser, Telegraph. A telegraphic receiver giving raised characters on a piece of paper. It generally refers to an apparatus of the old Morse receiver type, one using a dry point stylus, which pressing the paper into a groove in the roller above the paper, gave raised characters in dots and lines.

Fig. 163. MORSE RECEIVER.

238 STANDARD ELECTRICAL DICTIONARY.

E. M. D. P. Abbreviation for "electro-motive difference of potential" or for electro-motive force producing a current as distinguished from mere inert potential difference.

E. M. F. Abbreviation for "electro-motive force."

Fig. 164. END-ON METHOD.

End-on Method. A method of determining the magnetic moment of a magnet. The magnet under examination, N S, is placed at right angles to the magnetic meridian, M O R, and pointing directly at or "end on" to the centre of a compass needle, n s. From the deflection a of the latter the moment is calculated.

Endosmose, Electric. The inflowing current of electric osmose. (See Osmose, Electric.)

End Play. The power to move horizontally in its bearings sometimes given to armature shafts. This secures a more even wearing of the commutator faces. End play is not permissible in disc armatures, as the attraction of the field upon the face of the armature core would displace it endwise. For such armatures thrust-bearings preventing end play have to be provided.

Energy. The capacity for doing work. It is measured by work units which involve the exercise of force along a path of some length. A foot-pound, centimeter-gram, and centimeter-dyne are units of energy and work.

The absolute unit of energy is the erg, a force of one dyne exercised over one centimeter of space. (See Dyne.)

The dimensions of energy are force (M * L / T^2) * space (L) = M * (L^2 / T^2). Energy may be chemical (atomic or molecular), mechanical, electrical, thermal, physical, potential, kinetic, or actual, and other divisions could be formulated.

239 STANDARD ELECTRICAL DICTIONARY.

Energy, Atomic. The potential energy due to atomic relations set free by atomic change; a form of chemical energy, because chemistry refers to molecular as well as to atomic changes. When atomic energy loses the potential form it immediately manifests itself in some other form, such as heat or electric energy. It may be considered as always being potential energy. (See Energy, Chemical.)

[Transcriber's note: This item refers to chemical energy, that is manifest in work done by electric forces during re-arrangement of electrons. Atomic energy now refers to re-arrangement of nucleons (protons and neutrons) and the resulting conversion of mass into energy.]

Energy, Chemical. A form of potential energy (see Energy, Potential) possessed by elements in virtue of their power of combining with liberation of energy, as in the combination of carbon with oxygen in a furnace; or by compounds in virtue of their power of entering into other combinations more satisfying to the affinities of their respective elements or to their own molecular affinity. Thus in a galvanic couple water is decomposed with absorption of energy, but its oxygen combines with zinc with evolution of greater amount of energy, so that in a voltaic couple the net result is the setting free of chemical energy, which is at once converted into electrical energy in current form, if the battery is on a closed circuit.

Energy, Conservation of. A doctrine accepted as true that the sum of energy in the universe is fixed and invariable. This precludes the possibility of perpetual motion. Energy may be unavailable to man, and in the universe the available energy is continually decreasing, but the total energy is the same and never changes.

[Transcriber's note: If mass is counted a energy (E=m*(c^2)) then energy is strictly conserved.]

Energy, Degradation of. The reduction of energy to forms in which it cannot be utilized by man. It involves the reduction of potential energy to kinetic energy, and the reduction of kinetic energy of different degrees to energy of the same degree. Thus when the whole universe shall have attained the same temperature its energy will have become degraded or non-available. At present in the sun we have a source of kinetic energy of high degree, in coal a source of potential energy. The burning of all the coal will be an example of the reduction of potential to kinetic energy, and the cooling of the sun will illustrate the lowering in degree of kinetic energy. (See Energy, Conservation of--Energy, Potential--Energy, Kinetic.)

Energy, Electric. The capacity for doing work possessed by electricity under proper conditions. Electric energy may be either kinetic or potential. As ordinary mechanical energy is a product of force and space, so electric energy is a product of potential difference and quantity. Thus a given number of coulombs of electricity in falling a given number of volts develop electric energy. The dimensions are found therefore by multiplying electric current intensity quantity ((M^.5) * (L^.5)), by electric potential ((M^.5)*(L^1.5) / (T^2)), giving (M * (L^2)/(T^2)), the dimensions of energy in general as it should be.

The absolute unit of electric energy in electro-magnetic measure is (1E-7) volt coulombs.

240 STANDARD ELECTRICAL DICTIONARY.

The practical unit is the volt-coulomb. As the volt is equal to 1E8 absolute units of potential and the coulomb to 0.1 absolute units of quantity, the volt-coulomb is equal to 1E7 absolute units of energy.

The volt-coulomb is very seldom used, and the unit of Electric Activity or Power (see Power, Electric), the volt-ampere, is universally used. This unit is sometimes called the Watt, q. v., and it indicates the rate of expenditure or of production of electric energy.

The storing up in a static accumulator or condenser of a given charge of electricity, available for use with a given change of potential represents potential electric energy.

The passing of a given quantity through a conductor with a given fall of potential represents kinetic electric energy.

In a secondary battery there is no storage of energy, but the charging current simply accumulates potential chemical energy in the battery, which chemical energy is converted into electric energy in the discharge or delivery of the battery.

It is customary to discuss Ohm's law in this connection; it is properly treated under Electric Power, to which the reader is referred. (See Power, Electric.)

[Transcriber's note: A volt-ampere or watt is a unit of power. A volt-coulomb second or watt-second is a unit of energy. Power multiplied by time yields energy.]

Energy, Electric Transmission of. If an electric current passes through a conductor all its energy is expended in the full circuit. Part of the circuit may be an electrical generator that supplies energy as fast as expended. Part of the circuit may be a motor which absorbs part of the energy, the rest being expended in forcing a current through the connecting wires and through the generator. The electric energy in the generator and connecting wires is uselessly expended by conversion into heat. That in the motor in great part is utilized by conversion into mechanical energy which can do useful work. This represents the transmission of energy. Every electric current system represents this operation, but the term is usually restricted to the transmission of comparatively large quantities of energy.

A typical installation might be represented thus. At a waterfall a turbine water wheel is established which drives a dynamo. From the dynamo wires are carried to a distant factory, where a motor or several motors are established, which receive current from the dynamo and drive the machinery. The same current, if there is enough energy, may be used for running lamps or electroplating. As electric energy (see Energy, Electric,) is measured by the product of potential difference by quantity, a very small wire will suffice for the transmission of a small current at a high potential, giving a comparatively large quantity of energy. It is calculated that the energy of Niagara Falls could be transmitted through a circuit of iron telegraph wire a distance of over 1,000 miles, but a potential difference of 135,000,000 volts would be required, something quite impossible to obtain or manage.

[Transcriber's note: Contemporary long distance power transmission lines use 115,000 to 1,200,000 volts. At higher voltages corona discharges (arcing) create unacceptable losses.]

241 STANDARD ELECTRICAL DICTIONARY.

Energy, Kinetic. Energy due to matter being actually in motion. It is sometimes called actual energy. The energy varies directly with the mass and with the square of the velocity. It is represented in formula by .5 *M * (v^2).

Synonyms--Actual Energy--Energy of Motion--Dynamic Energy.

Energy, Mechanical. The energy due to mechanical change or motion, virtually the same as molar energy. (See Energy, Molar.)

Energy, Molar. The energy of masses of matter due to movements of or positions of matter in masses; such as the kinetic energy of a pound or of a ton in motion, or the potential energy of a pound at an elevation of one hundred feet.

Energy, Molecular. The potential energy due to the relations of molecules and set free by their change in the way of combination. It is potential for the same reason that applies to atomic and chemical energy, of which latter it is often a form, although it is often physical energy. The potential energy stored up in vaporization is physical and molecular energy; the potential energy stored up in uncombined potassium oxide and water, or calcium oxide (quicklime) and water is molecular, and when either two substances are brought together kinetic, thermal or heat energy is set free, as in slaking lime for mortar.

Energy of an Electrified Body. An electrified body implies the other two elements of a condenser. It is the seat of energy set free when discharged. (See Dielectric, Energy of.) The two oppositely charged bodies tend to approach. This tendency, together with the distances separating them, represents a potential energy.