Chapter C: G. S (3)

Current, Pulsatory. A current of constant direction, but whose strength is constantly varying, so that it is a series of pulsations of current instead of a steady flow.

Current, Rectified. A typical alternating current is represented by a sine curve, whose undulations extend above and below the zero line. If by a simple two member commutator the currents are caused to go in one direction, in place of the sine curve a series of short convex curves following one another and all the same side of the zero line results. The currents all in the same direction, become what is known as a pulsating current.

Synonym--Redressed Current.

165 STANDARD ELECTRICAL DICTIONARY.

Current, Rectilinear. A current flowing through a rectilinear conductor. The action of currents depending on their distance from the points where they act, their contour is a controlling factor. This contour is determined by the conductors through which they flow.

Current Reverser. A switch or other contrivance for reversing the direction of a current in a conductor.

Currents, Ampérian. The currents of electricity assumed by Ampere's theory to circulate around a magnet. As they represent the maintenance of a current or of currents without the expenditure of energy they are often assumed to be of molecular dimensions. As they all go in the same sense of rotation and are parallel to each other the result is the same as if a single set of currents circulated around the body of the magnet. More will be found on this subject under Magnetism. The Ampérian currents are purely hypothetical and are predicated on the existence of a field of force about a permanent magnet. (See Magnetism, Ampére's Theory of.)

If the observer faces the north pole of a magnet the Ampérian currents are assumed to go in the direction opposite to that of a watch, and the reverse for the south pole.

Figs. 118-119 DIRECTION OF AMPÉRIAN CURRENTS.

Currents, Angular. Currents passing through conductors which form an angle with each other.

Currents, Angular, Laws of. 1. Two rectilinear currents, the directions of which form an angle with each other, attract one another when both approach to or recede from the apex of the angle.

2. They repel one another, if one approaches and the other recedes from the apex of the angle.

166 STANDARD ELECTRICAL DICTIONARY

Currents, Earth. In long telegraph lines having terminal grounds or connected to earth only at their ends, potential differences are sometimes observed that are sufficient to interfere with their working and which, of course, can produce currents. These are termed earth-currents. It will be noted that they exist in the wire, not in the earth. They may be of 40 milliamperes strength, quite enough to work a telegraph line without any battery. Lines running N. E. and S. W. are most affected; those running N.W. and S. E. very much less so. These currents only exist in lines grounded at both ends, and appear in underground wires. Hence they are not attributable to atmospheric electricity. According to Wilde they are the primary cause of magnetic storms, q. v., but not of the periodical changes in the magnetic elements. (See Magnetic Elements.)

Synonym--Natural Currents.

Current, Secondary. (a) A current induced in one conductor by a variation in the current in a neighboring one; the current produced in the secondary circuit of an induction coil or alternating current converter.

(b) The current given by a secondary battery. This terminology is not to be recommended.

Current, Secretion. In electro-therapeutics, a current due to stimulation of the secretory nerves.

Current Sheet. (a) If two terminals of an active circuit are connected to two points of a thin metallic plate the current spreads over or occupies practically a considerable area of such plate, and this portion of the current is a current sheet.

The general contour of the current sheet can be laid out in lines of flux. Such lines resemble lines of force. Like the latter, they are purely an assumption, as the current is not in any sense composed of lines.

(b) A condition of current theoretically brought about by the Ampérian currents in a magnet. Each molecule having its own current, the contiguous portions of the molecules counteract each other and give a resultant zero current. All that remains is the outer sheet of electric current that surrounds the whole.

Current, Sinuous. A current passing through a sinuous conductor.

Currents, Multiphase. A term applied to groups of currents of alternating type which constantly differ from each other by a constant proportion of periods of alternation. They are produced on a single dynamo, the winding being so contrived that two, three or more currents differing a constant amount in phase are collected from corresponding contact rings. There are virtually as many windings on the armature as there are currents to be produced. Separate conductors for the currents must be used throughout.

Synonyms--Polyphase Currents--Rotatory Currents.

167 STANDARD ELECTRICAL DICTIONARY.

Currents of Motion. In electro-therapeutics, the currents produced in living muscle or nerves after sudden contraction or relaxation.

Currents of Rest. In electro-therapeutics, the currents traversing muscular or nervous tissue when at rest. Their existence is disputed.

Currents, Orders of. An intermittent current passing through a conductor will induce secondary alternating currents in a closed circuit near it. This secondary current will induce a tertiary current in a third closed circuit near it, and so on. The induced currents are termed as of the first, second, third and other orders. The experiment is carried out by Henry's coils. (See Coils, Henry's.)

Currents, Thermo-electric. These currents, as produced from existing thermo-electric batteries, are generated by low potential, and are of great constancy. The opposite junctions of the plates can be kept at constant temperatures, as by melting ice and condensing steam, so that an identical current can be reproduced at will from a thermopile.

Thermo-electric currents were used by Ohm in establishing his law. (See Ohm's Law.)

Current, Swelling. In electro-therapeutics, a current gradually increasing in strength.

Current, Undulatory. A current varying in strength without any abrupt transition from action to inaction, as in the make and break current. The current may be continually changing in direction (see Current, Alternating), and hence, of necessity, may pass through stages of zero intensity, but such transition must be by a graduation, not by an abrupt transition. Such current may be represented by a curve, such as the curve of sines. It is evident that the current may pass through the zero point as it crosses the line or changes direction without being a make and break current. When such a current does alternate in direction it is sometimes called a "shuttle current." The ordinary commercial telephone current and the alternating current is of this type. (See Current, Make and Break.)

Current, Unit. Unit current is one which in a wire of unit length, bent so as to form an arc of a circle of unit length of radius, would act upon a unit pole (see Magnetic Pole, Unit,) at the center of the circle with unit force. Unit length is the centimeter; unit force is the dyne.

[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.]

168 STANDARD ELECTRICAL DICTIONARY.

Current, Wattless. Whenever there is a great difference in phase in an alternating current dynamo between volts and current, the true watts are much less than the product of the virtual volts and amperes, because the the watts are obtained by multiplying the product of the virtual volts and amperes by the cosine of the angle of lag (or lead). Any alternating current may be resolved into two components in quadrature with each other, one in phase with the volts, the other in quadrature therewith, the former is termed by S. P. Thompson the Working Current, the latter the Wattless Current. The greater the angle of lag the greater will be the wattless current.

Curve, Arrival. A curve representing the rate of rise of intensity of current at the end of a long conductor when the circuit has been closed at the other end. In the Atlantic cable, for instance, it would require about 108 seconds for the current at the distant end to attain 9/10 of its full value. The curve is drawn with its abscissa representing time and its ordinates current strength.

Curve, Characteristic. A curve indicating, graphically, the relations between any two factors, which are interdependent, or which vary simultaneously. Thus in a dynamo, the voltage increases with the speed of rotation, and a characteristic curve may be based on the relations between the speed of rotation and voltage developed. The current produced by a dynamo varies with the electro-motive force, and a curve can express the relations between the electro-motive force and the current produced.

A characteristic curve is usually laid out by rectangular co-ordinates (see Co-ordinates). Two lines are drawn at right angles to each other, one vertical, and the other horizontal. One set of data are marked off on the horizontal line, say one ampere, two amperes, and so on, in the case of a dynamo's characteristic curve.

For each amperage of current there is a corresponding voltage in the circuit. Therefore on each ampere mark a vertical is erected, and on that the voltage corresponding to such amperage is laid off. This gives a series of points, and these points may be connected by a curve. Such curve will be a characteristic curve.

The more usual way of laying out a curve is to work directly upon the two axes. On one is laid off the series of values of one set of data; on the other the corresponding series of values of the other dependent data. Vertical lines or ordinates, q. v., are erected on the horizontal line or axis of abscissas at the points laid off; horizontal lines or abscissas, q. v., are drawn from the points laid off on the vertical line or axis of ordinates. The characteristic curve is determined by the intersections of each corresponding pair of abscissa and ordinate.

169 STANDARD ELECTRICAL DICTIONARY.

Variations exist in characteristic curve methods. Thus to get the characteristic of a commutator, radial lines may be drawn from a circle representing its perimeter. Such lines may be of length proportional to the voltage developed on the commutator at the points whence the lines start. A cut giving an example of such a curve is given in Fig. 125. (See Curve of Distribution of Potential in Armature.)

There is nothing absolute in the use of ordinates or abscissas. They may be interchanged. Ordinarily voltages are laid off as ordinates, but the practise may be reversed. The same liberty holds good for all characteristic curves. Custom, however, should be followed.

Synonym--Characteristic.

Fig. 120. CHARACTERISTIC CURVE OF A DYNAMO WITH HORSE POWER CURVES.

Curve, Characteristic, of Converter. The characteristic curve of the secondary circuit of an alternating current converter. It gives by the usual methods (see Curve, Characteristic,) the relations between the electro-motive force and the current in the secondary circuit at a fixed resistance. If connected in parallel a constant electro-motive force is maintained, and the curve is virtually a straight line. If connected in series an elliptical curve is produced.

170 STANDARD ELECTRICAL DICTIONARY.

Curve, Charging. In secondary battery manipulation, a curve indicating the increase of voltage as the charging is prolonged. The rise in voltage with the duration of the charging current is not uniform. In one case, shown in the cut, there was a brief rapid rise of about 0.1 volt; then a long slow rise for 0.15 volt; then a more rapid rise for nearly 0.40 volt, and then the curve became a horizontal line indicating a cessation of increase of voltage. The charging rate should be constant.

The horizontal line is laid off in hours, the vertical in volts, so that the time is represented by abscissas and the voltage by ordinates of the curve.

Fig. 121. CHARGING CURVE OF A SECONDARY BATTERY.

Curve, Discharging. A characteristic curve of a storage battery, indicating the fall in voltage with hours of discharge. The volts may be laid off on the axis of ordinates, and the hours of discharging on the axis of abscissas. To give it meaning the rate of discharge must be constant.

Curve, Electro-motive Force. A characteristic curve of a dynamo. It expresses the relation between its entire electromotive force, as calculated by Ohm's Law, and the current intensities corresponding thereto. To obtain the data the dynamo is driven with different resistances in the external circuit and the current is measured for each resistance. This gives the amperes. The total resistance of the circuit, including that of the dynamo, is known. By Ohm's Law the electro-motive force in volts is obtained for each case by multiplying the total resistance of the circuit in ohms by the amperes of current forced through such resistance. Taking the voltages thus calculated for ordinates and the corresponding amperages for abscissas the curve is plotted. An example is shown in the cut.

171 STANDARD ELECTRICAL DICTIONARY.

Curve, External Characteristic. A characteristic curve of a dynamo, corresponding to the electro-motive force curve, except that the ordinates represent the voltages of the external circuit, the voltages as taken directly from the terminals of the machine, instead of the total electro-motive force of the circuit. The dynamo is run at constant speed. The resistance of the external circuit is varied. The voltages at the terminals of the machine and the amperages of current corresponding thereto are determined. Using the voltages thus determined as ordinates and the corresponding amperages as abscissas the external characteristic curve is plotted.

This curve can be mechanically produced. A pencil may be moved against a constant force by two electro-magnets pulling at right angles to each other. One must be excited by the main current of the machine, the other by a shunt current from the terminals of the machine. The point of the pencil will describe the curve.

Fig. 122. CHARACTERISTIC CURVE OF A DYNAMO.

Curve, Horse Power. Curves indicating electric horse power. They are laid out with co-ordinates, volts being laid off on the axis of ordinates, and amperes on the axis of abscissas generally. The curves are drawn through points where the product of amperes by volts equals 746. On the same diagram 1, 2, 3 .... and any other horse powers can be plotted if within the limits. See Fig. 120.

Curve, Isochasmen. A line drawn on the map of the earth's surface indicating the locus of equal frequency of auroras.

172 STANDARD ELECTRICAL DICTIONARY.

Curve, Life. A characteristic curve showing the relations between the durability and conditions affecting the same in any appliance. It is used most for incandescent lamps. The hours of burning before failure give ordinates, and the rates of burning, expressed indirectly in volts or in candle-power, give abscissas. For each voltage or for each candle-power an average duration is deducible from experience, so that two dependent sets of data are obtained for the construction of the curve.

Curve, Load. A characteristic curve of a dynamo, expressing the relation between its voltage and the amount of excitation under a definite condition of ampere load, at a constant speed. The ordinates represent voltage, the abscissas ampere turns in the field, and the curves may be constructed for a flow of 0, 50, 100, or .. , or any other number of amperes.

Fig. 123. LOAD CURVES.

Curve, Magnetization. A characteristic curve of an electromagnet, indicating the relation of magnetization to exciting current. Laying off on the axis of ordinates the quantities of magnetism evoked, and the corresponding strengths of the exciting current on the axis of abscissas, the curve can be plotted. It first rises rapidly, indicating a rapid increase of magnetization, but grows nearly horizontal as the iron becomes more saturated. The effect due to the coils alone, or the effect produced in the absence of iron is a straight line, because air does not change in permeability.

Curve of Distribution of Potential in Armature. A characteristic curve indicating the distribution of potential difference between adjoining sections of the commutator of an armature in different positions all around it. The potential differences are taken by a volt-meter or potential galvanometer, connection with the armature being made by two small metal brushes, held at a distance apart equal to the distance from centre to centre of two adjoining commutator bars. The curve is laid out as if by polar co-ordinates extending around the cross-section of the commutator, with the distances from the commutator surface to the curve proportional to the potential differences as determined by shifting the pair of brushes all around the commutator.

The above is S. P. Thompson's method. Another method of W. M. Mordey involves the use of a pilot brush. (See Brush, Pilot.) Otherwise the method is in general terms identical with the above.

173 STANDARD ELECTRICAL DICTIONARY.

Fig. 124. MAGNETIZATION CURVE.

Fig. 125. ARMATURE: CURVE.

Fig. 126. DEVELOPMENT OF ARMATURE CURVE.

Curve of Dynamo. The characteristic curve of a dynamo. (See Curve, Characteristic.)

Curve of Sines. An undulating curve representing wave motion. It is produced by compounding a simple harmonic motion, or a two and fro motion like that of an infinitely long pendulum with a rectilinear motion. Along a horizontal line points may be laid off to represent equal periods of time. Then on each point a perpendicular must be erected. The length of each must be equal to the length of path traversed by the point up to the expiration of each one of the given intervals of time. The abscissas are proportional to the times and the ordinates to the sines of angles proportional to the times. Thus if a circle be drawn upon the line and divided into thirty-two parts of equal angular value, the sines of these angles may be taken as the ordinates and the absolute distance or length of arc of the angle will give the abscissas.

Synonyms--Sine Curve--Sinusoidal Curve--Harmonic Curve.

Fig. 127. CURVE OF SINES.

174 STANDARD ELECTRICAL DICTIONARY.

Curve of Saturation of the Magnetic Circuit. A characteristic curve whose ordinates may represent the number of magnetic lines of force induced in a magnetic circuit, and whose abscissas may represent the ampere turns of excitation or other representative of the inducing force.

Curve of Torque. A characteristic curve showing the relations between torque, q. v., and current in a dynamo or motor.

Curve, Permeability Temperature. A characteristic curve expressing the changes in permeability of a paramagnetic substance as the temperature changes. The degrees of temperature may be abscissas, and the permeabilities corresponding thereto ordinates of the curve.

Cut In. v. To connect any electric appliance, mechanism or conductor, into a circuit.

Cut Out. v. The reverse of to cut in; to remove from a circuit any conducting device, and sometimes so arranged as to leave the circuit completed in some other way.

Cut Out. An appliance for removing any apparatus from an electric circuit, so that no more current shall pass through such apparatus, and sometimes providing means for closing the circuit so as to leave it complete after the removal of the apparatus.

175 STANDARD ELECTRICAL DICTIONARY.

Cut Out, Automatic. (a) A mechanism for automatically shunting an arc or other lamp when it ceases to work properly. It is generally worked by an electro-magnet of high resistance placed in parallel with the arc. If the arc grows too long the magnet attracts its armature, thereby completing a shunt of approximately the resistance of the arc, and which replaces it until the carbons approach again to within a proper distance. Sometimes a strip or wire of fusible metal is arranged in shunt with the arc. When the arc lengthens the current through the wire increases, melts it and a spring is released which acts to complete or close a shunt circuit of approximately arc-resistance.

(b) See Safety Device--Safety Fuse.

(c) See below.

Cut-out, Magnetic. A magnetic cut-out is essentially a coil of wire with attracted core or armature. When the coil is not excited the core, by pressing down a strip of metal or by some analogous arrangement, completes the circuit. When the current exceeds a certain strength the core rises as it is attracted and the circuit is opened.

Cut-out, Safety. A block of porcelain or other base carrying a safety fuse, which melts and breaks the circuit before the wire connected to it is dangerously heated.

Synonyms--Fuse Block--Safety Catch--Safety Fuse.

Cut Out, Wedge. A cut out operated by a wedge. The line terminals consist of a spring bearing against a plate, the circuit being completed through their point of contact. A plug or wedge composed of two metallic faces insulated from each other is adapted to wedge the contact open. Terminals of a loop circuit are connected to the faces of the wedge. Thus on sliding it into place, the loop circuit is brought into series in the main circuit.

Synonym--Plug Cut Out--Spring Jack.

Cutting of Lines of Force. A field of force is pictured as made up of lines of force; a conductor swept through the field is pictured as cutting these lines. By so doing it produces potential difference or electro-motive force in itself with a current, if the conductor is part of a closed circuit.

Cycle of Alternation. A full period of alternation of an alternating current. It begins properly at the zero line, goes to a maximum value in one sense and returns to zero, goes to maximum in the other sense and returns to zero.

Cystoscopy. Examination of the human bladder by the introduction of a special incandescent electric lamp. The method is due to Hitze.

176 STANDARD ELECTRICAL DICTIONARY.

Damper. (a) A copper frame on which the wire in a galvanometer is sometimes coiled, which acts to damp the oscillations of the needle.

(b) A tube of brass or copper placed between the primary and secondary coils of an induction coil. It cuts off induction and diminishes the current and potential of the secondary circuit. On pulling it out, the latter increases. It is used on medical coils to adjust their strength of action.

Damping. Preventing the indicator of an instrument from oscillating in virtue of its own inertia or elasticity. In a galvanometer it is defined as resistance to quick vibrations of the needle, in consequence of which it is rapidly brought to rest when deflected (Ayrton). In dead-beat galvanometers (see Galvanometer, Dead-Beat,) damping is desirable in order to bring the needle to rest quickly; in ballistic galvanometers (see Galvanometer, Ballistic,) damping is avoided in order to maintain the principle of the instrument. Damping may be mechanical, the frictional resistance of air to an air-vane, or of a liquid to an immersed diaphragm or loosely fitting piston, being employed. A dash-pot, q. v., is an example of the latter. It may be electro-magnetic. A mass of metal near a swinging magnetic needle tends by induced currents to arrest the oscillations thereof, and is used for this purpose in dead-beat galvanometers. This is termed, sometimes, magnetic friction. The essence of damping is to develop resistance to movement in some ratio proportional to velocity, so that no resistance is offered to the indicator slowly taking its true position. (See Galvanometer, Dead-Beat.)

Dash-Pot. A cylinder and piston, the latter loosely fitting or perforated, or some equivalent means being provided to permit movement. The cylinder may contain a liquid such as glycerine, or air only. Thus the piston is perfectly free to move, but any oscillations are damped (see Damping). In some arc lamps the carbon holder is connected to a dash-pot to check too sudden movements of the carbon. The attachment may be either to the piston or to the cylinder. In the Brush lamp the top of the carbon holder forms a cylinder containing glycerine, and in it a loosely fitting piston works. This acts as a dash-pot.

Dead Beat. adj. Reaching its reading quickly; applied to instruments having a moving indicator, which normally would oscillate back and forth a number of times before reaching its reading were it not prevented by damping. (See Galvanometer, Aperiodic--Damping.)

Dead Earth. A fault in a telegraph line which consists in the wire being thoroughly grounded or connected to the earth.

177 STANDARD ELECTRICAL DICTIONARY.

Dead Point of an Alternator. A two-phase alternator of the ordinary type connected as a motor to another alternator cannot start itself, as it has dead points where the relations and polarity of field and armature are such that there is no torque or turning power.

Dead-Turns. In the winding of an armature, a given percentage of the turns, it may be 80 per cent., more or less, is assumed to be active; the other 20 per cent. or thereabouts, is called dead-turns. This portion represents the wire on such portions of the armature as comes virtually outside of the magnetic field. They are termed dead, as not concurring to the production of electro-motive force.

Dead Wire. (a) The percentage or portion of wire on a dynamo or motor armature that does not concur in the production of electromotive force. The dead-turns, q. v., of a drum armature or the inside wire in a Gramme ring armature are dead wire.

(b) A disused and abandoned electric conductor, such as a telegraph wire.

(c) A wire in use, but through which, at the time of speaking, no current is passing.

Death, Electrical. Death resulting from electricity discharged through the animal system. The exact conditions requisite for fatal results have not been determined. High electro-motive force is absolutely essential; a changing current, pulsatory or alternating, is most fatal, possibly because of the high electro-motive force of a portion of each period. Amperage probably has something to do with it, although the total quantity in coulombs may be very small. As applied to the execution of criminals, the victim is seated in a chair and strapped thereto. One electrode with wet padded surface is placed against his head or some adjacent part. Another electrode is placed against some of the lower parts, and a current from an alternating dynamo passed for 15 seconds or more. The potential difference of the electrodes is given at 1,500 to 2,000 volts, but of course the maximum may be two or three times the measured amount, owing to the character of the current.

Decalescence. The converse of recalescence, q. v. When a mass of steel is being heated as it reaches the temperature of recalescence it suddenly absorbs a large amount of heat, apparently growing cooler.

Deci. Prefix originally used in the metric system to signify one-tenth of, now extended to general scientific units. Thus decimeter means one-tenth of a meter; decigram, one-tenth of a gram.

Declination, Angle of. The angle intercepted between the true meridian and the axis of a magnetic needle at any place. The angle is measured to east or west, starting from the true meridian as zero.

178 STANDARD ELECTRICAL DICTIONARY.

Declination of the Magnetic Needle. The deviation of the magnetic needle from the plane of the earth's meridian. It is also called the variation of the compass. (See Magnetic Elements.)

Decomposition. The reduction of a compound substance into its constituents, as in chemical analysis. The constituents may themselves be compounds or proximate constituents, or may be elemental or ultimate constituents.

Decomposition, Electrolytic. The decomposition or separation of a compound liquid into its constituents by electrolysis. The liquid must be an electrolyte, q. v., and the decomposition proceeds subject to the laws of electrolysis, q. v. See also Electrolytic Analysis.

Decrement. When a suspension needle which has been disturbed is oscillating the swings gradually decrease in amplitude if there is any damping, as there always is. The decrement is the ratio of the amplitude of one oscillation to the succeeding one. This ratio is the same for any successive swings.

De-energize. To cut off its supply of electric energy from an electric motor, or any device absorbing and worked by electric energy.

Deflagration. The explosive or violent volatilizing and dissipating of a substance by heat, violent oxidation and similar means. It may be applied among other things to the destroying of a conductor by an intense current, or the volatilization of any material by the electric arc.

Deflecting Field. The field produced in a galvanometer by the current which is being tested, and which field deflects the needle, such deflection being the measure of the current strength.

Deflection. In magnetism the movement out of the plane of the magnetic meridian of a magnetic needle, due to disturbance by or attraction towards a mass of iron or another magnet.

Deflection Method. The method of electrical measurements in which the deflection of the index of the measuring instrument is used as the measure of the current or other element under examination. It is the opposite of and is to be distinguished from the zero or null method, q. v. In the latter conditions are established which make the index point to zero and from the conditions necessary for this the measurement is deduced. The Wheatstone Bridge, q. v., illustrates a zero method, the sine or the tangent compass, illustrates a deflection method. The use of deflection methods involves calibration, q. v., and the commercial measuring instruments, such as ammeters and volt meters, which are frequently calibrated galvanometers, are also examples of deflection instruments.

179 STANDARD ELECTRICAL DICTIONARY.

Degeneration, Reaction of. The diminished sensibility to electro-therapeutic treatment exhibited by the human system with continuance of the treatment in question. The general lines of variation are stated in works on the subject.

Deka. Prefix originally used in the metric system to signify multiplying by ten, as dekameter, ten meters, dekagram, ten grams; now extended to many scientific terms.

De la Rive's Floating Battery. A small galvanic couple, immersed in a little floating cell and connected through a coil of wire immediately above them. When the exciting battery solution is placed in the cell the whole, as it floats in a larger vessel, turns until the coil lies at right angles to the magnetic needle. Sometimes the two plates are thrust through a cork and floated thus in a vessel of dilute sulphuric acid.

A magnet acts to attract or repel the coil in obedience to Ampére's Theory, (See Magnetism, Ampere's Theory of.)

Delaurier's Solution.
A solution for batteries of the Bunsen and Grenet type. It is of the
following composition:
Water, 2,000 parts;
potassium bichromate, 184 parts;
sulphuric acid, 428 parts.

Demagnetization. Removal of magnetism from a paramagnetic substance. It is principally used for watches which have become magnetized by exposure to the magnetic field surrounding dynamos or motors.

The general principles of most methods are to rotate the object, as a watch, in a strong field, and while it is rotating to gradually remove it from the field, or to gradually reduce the intensity of the field itself to zero. A conical coil of wire within which the field is produced in which the watch is placed is sometimes used, the idea being that the field within such a coil is strongest at its base. Such a coil supplied by an alternating current is found effectual (J. J. Wright).

If a magnetized watch is made to turn rapidly at the end of a twisted string and is gradually brought near to and withdrawn from the poles of a powerful dynamo it may be considerably improved.

A hollow coil of wire connected with a pole changer and dip-battery has been used. The battery creates a strong field within the coil. The watch is placed there and the pole changer is worked so as to reverse the polarity of the field very frequently. By the same action of the pole changer the plates of the battery are gradually withdrawn from the solution so as to gradually reduce the magnetic field to zero while constantly reversing its polarity. (G. M. Hopkins.)

Steel may be demagnetized by jarring when held out of the magnetic meridian, or by heating to redness.

180 STANDARD ELECTRICAL DICTIONARY.

Density, Electric Superficial. The relative quantity of electricity residing as an electric charge upon a unit area of surface. It may be positive or negative.

Synonyms--Density of Charge--Surface Density.

Dental Mallet, Electric. A dentist's instrument for hammering the fillings as inserted into teeth. It is a little hammer held in a suitable handle, and which is made to strike a rapid succession of blows by electro-magnetic motor mechanism.

Depolarization. (a) The removal of permanent magnetism. (See Demagnetization.)

(b) The prevention of the polarization of a galvanic cell. It is effected in the Grove battery by the reduction of nitric acid; in the Bunsen, by the reduction of chromic acid; in the Smee battery, mechanically, by the platinum coated or rather platinized negative plate. Other examples will be found under the description of various cells and batteries. A fluid which depolarizes is termed a depolarizer or depolarizing fluid or solution. (See Electropoion Fluid.)

Deposit, Electrolytic. The metal or other substance precipitated by the action of a battery or other current generator.

Derivation, Point of. A point where a circuit branches or divides into two or more leads. The separate branches then receive derived or partial currents.

Desk Push. A press or push button, with small flush rim, for setting into the woodwork of a desk.

Detector. A portable galvanometer, often of simple construction, used for rough or approximate work.

Detector, Lineman's. A portable galvanometer with a high and a low resistance actuating coil, constructed for the use of linemen and telegraph constructors when in the field, and actually putting up, repairing or testing lines.

Deviation, Quadrantal. Deviation of the compass in iron or steel ships due to the magnetization of horizontal beams by the earth's induction. The effect of this deviation disappears when the ship is in the plane of the electric meridian, or at right angles thereto; its name is taken from the fact that a swing of the ship through a quadrant brings the needle from zero deviation to a maximum and back to zero.

181 STANDARD ELECTRICAL DICTIONARY.

Deviation, Semicircular. Deviation of the compass in iron or steel ships due to vertical induction. (See Induction, Vertical.) The effect of this induction disappears when the ship is in the electric meridian. Its name is derived from the fact that a swing of the ship through half the circle brings the needle from zero deviation to a maximum and back to zero.

Dextrotorsal. adj. Wound in the direction or sense of a right-handed screw; the reverse of sinistrotorsal, q. v.

Fig. 128. DEXTROTORSAL HELIX.

Diacritical. adj. (a) The number of ampere turns, q. v., required to bring an iron core to one half its magnetic saturation, q. v., is termed the diacritical number.

(b) The diacritical point of magnetic saturation is proposed by Sylvanus P. Thompson as a term for the coefficient of magnetic saturation which gives a magnet core one-half its maximum magnetization.

Diagnosis, Electro. A medical diagnosis of a patient's condition based on the action of different parts of the body under electric excitement.

Diamagnetic. adj. Possessing a negative coefficient of magnetic susceptibility; having permeability inferior to that of air. Such substances placed between the poles of a magnet are repelled; if in the form of bars, they tend to turn so as to have their long axis at right angles to the line joining the poles. The reason is that the lines of force always seek the easiest path, and these bodies having higher reluctance than air, impede the lines of force, and hence are as far as possible pushed out of the way. The above is the simplest explanation of a not well understood set of phenomena. According to Tyndall, "the diamagnetic force is a polar force, the polarity of diamagnetic bodies being opposed to that of paramagnetic ones under the same conditions of excitement." Bismuth is the most strongly diamagnetic body known; phosphorus, antimony, zinc, and many others are diamagnetic. (See Paramagnetic.)

182 STANDARD ELECTRICAL DICTIONARY.

Diagometer. An apparatus for use in chemical analysis for testing the purity of substances by the time required for a charged surface to be discharged through them to earth. It is the invention of Rousseau.

An electrometer is charged with a dry pile. One of its terminals is connected with one surface of the solution or substance to be tested, and the other with the other surface. The time of discharge gives the index of the purity of the substance.

Diamagnetic Polarity. Treating diamagnetism as due to a polar force, the polarity of a diamagnetic body is the reverse of the polarity of iron or other paramagnetic bodies. A bar-shaped diamagnetic body in a field of force tends to place itself at right angles to the lines of force.

Diamagnetism. (a) The science or study of diamagnetic substances and phenomena.

(b) The magnetic property of a diamagnetic substance.

Diameter of Commutation. The points on the commutator of a closed circuit ring--or drum--armature, which the brushes touch, and whence they take the current, mark the extremities of the diameter of commutation. Were it not for the lag this would be the diameter at right angles to the line connecting the centers of the opposite faces of the field. It is always a little to one side of this position, being displaced in the direction of rotation. In open circuit armatures the brushes are placed on the diameter at right angles to this one, and sometimes the term diameter of commutation is applied to it. All that has been said is on the supposition that the armature divisions correspond not only in connection but in position with those of the armature coils. Of course, the commutator could be twisted so as to bring the diameter of commutation into any position desired.

Diapason, Electric. A tuning-fork or diapason kept in vibration by electricity. In general principle the ends of the fork act as armatures for an electro-magnet, and in their motion by a mercury cup or other form of contact they make and break the circuit as they vibrate. Thus the magnet alternately attracts and releases the leg, in exact harmony with its natural period of vibration.

Diaphragm. (a) In telephones and microphones a disc of iron thrown into motion by sound waves or by electric impulses, according to whether it acts as the diaphragm of a transmitter or receiver. It is generally a plate of japanned iron such as used in making ferrotype photographs. (See Telephone and Microphone.)

(b) A porous diaphragm is often used in electric decomposition cells and in batteries. The porous cup represents the latter use.

[Transcriber's note: Japanned--covered with heavy black lacquer, like enamel paint.]

183 STANDARD ELECTRICAL DICTIONARY.

Dielectric. A non-conductor; a substance, the different parts of which may, after an electric disturbance, remain, without any process of readjustment, and for an indefinite period of time, at potentials differing to any extent (Daniell). There is no perfect dielectric. The term dielectric is generally only used when an insulator acts to permit induction to take place through it, like the glass of a Leyden jar.

Dielectric Constant. The number or coefficient expressing the relative dielectric capacity of a medium or substance. (See Capacity, Specific Inductive.)

Dielectric, Energy of. In a condenser, the conducting coatings are merely to conduct the current all over the surface they cover; the keeping the electricities separated is the work of the dielectric, and represents potential energy which appears in the discharge. The amount of energy is proportional to the charge, and to the potential difference. As any electrified body implies an opposite electrification somewhere, and a separating dielectric, the existence of a condenser is always implied.

[Transcriber's note: The energy stored in a capacitor (condenser) is (Q*Q)/2C = (Q*V)/2 = (C*V*V)/2 The energy is proportional to the voltage SQUARED or the charge SQUARED.]

Dielectric Polarization. A term due to Faraday. It expresses what he conceived to be the condition of a dielectric when its opposite faces are oppositely electrified. The molecules are supposed to be arranged by the electrification in a series of polar chains, possibly being originally in themselves seats of opposite polarities, or having such imparted to them by the electricities. The action is analogous to that of a magnet pole on a mass of soft iron, or on a pile of iron filings.

Dielectric Strain. The strain a solid dielectric is subjected to, when its opposite surfaces are electrified. A Leyden jar dilates under the strain, and when discharged gives a dull sound. The original condition is not immediately recovered. Jarring, shaking, etc., assist the recovery from strain. The cause of the strain is termed Electric Stress. (See Stress, Electric.) This is identical with the phenomenon of residual charge. (See Charge, Residual.) Each loss of charge is accompanied with a proportional return of the dielectric towards its normal condition.

Dielectric Resistance. The mechanical resistance a body offers to perforation or destruction by the electric discharge.

Dielectric Strength. The resistance to the disruptive discharge and depending on its mechanical resistance largely or entirely. It is expressible in volts per centimeter thickness. Dry air requires 40,000 volts per centimeter for a discharge.

184 STANDARD ELECTRICAL DICTIONARY.

Differential Winding Working. A method of working an electro-magnet intermittently, so as to avoid sparking. The magnet is wound with two coils. One is connected straight into the circuit, the other is connected in parallel therewith with a switch inserted. The coils are so connected that when the switch is closed the two are in opposition, the current going through them in opposite senses. Thus one overcomes the effect of the other and the magnet core shows no magnetism, provided the two coils are of equal resistance and equal number of convolutions or turns.

Fig. 129. DIFFERENTIAL WINDING WORKING OF ELECTRO-MAGNETIC APPARATUS.

Diffusion. A term properly applied to the varying current density found in conductors of unequal cross sectional area. In electro-therapeutics it is applied to the distribution of current as it passes through the human body. Its density per cross-sectional area varies with the area and with the other factors.

Diffusion Creep. When electrodes of an active circuit are immersed in a solution of an electrolyte, a current passes electrolytically if there is a sufficient potential difference. The current passes through all parts of the solution, spreading out of the direct prism connecting or defined by the electrodes. To this portion of the current the above term is applied. If the electrodes are small enough in proportion to the distance between them the current transmission or creep outside of the line becomes the principal conveyor of the current so that the resistance remains the same for all distances.

Dimensions and Theory of Dimensions. The expression of the unitary value of a physical quantity in one or more of the units of length (L), time (T) and mass (M) is termed the dimensions of such quantity. Thus the dimension or dimensions of a distance is simply L; of an angle, expressible by dividing the arc by the radius is L/L; of a velocity, expressible by distance divided by time--L/T; of acceleration, which is velocity acquired in a unit of time, and is therefore expressible by velocity divided by time--L/T/T or L/T2; of momentum, which is the product of mass into velocity--M*L/T; of kinetic energy taken as the product of mass into the square of velocity--M*(L2/T2); of potential energy taken as the product of mass into acceleration into space-M*(L/T2)*L reducing to M*(L2/T2). The theory is based on three fundamental units and embraces all electric quantities. The simple units generally taken are the gram, centimeter and second and the dimensions of the fundamental compound units are expressed in terms of these three, forming the centimeter-gram-second or C. G. S. system of units. Unless otherwise expressed or implied the letters L, M and T, may be taken to indicate centimeter, gram and second respectively. It is obvious that very complicated expressions of dimensions may be built up, and that a mathematical expression of unnamed quantities may be arrived at. Dimensions in their application by these symbols are subject to the laws of algebra. They were invented by Fourier and were brought into prominence by J. Clerk Maxwell. Another excellent definition reads as follows: "By the dimensions of a physical quantity we mean the quantities and powers of quantities, involved in the measurement of it." (W. T. A. Emtage.)

185 STANDARD ELECTRICAL DICTIONARY.

Dimmer. An adjustable choking coil used for regulating the intensity of electric incandescent lights. Some operate by the introduction and withdrawal of an iron core as described for the choking coil (see Coil, Choking), others by a damper of copper, often a copper ring surrounding the coil and which by moving on or off the coil changes the potential of the secondary circuit.

Dip of Magnetic Needle. The inclination of the magnetic needle. (See Elements, Magnetic.)

Dipping. (a) Acid or other cleaning processes applied by dipping metals in cleaning or pickling solutions before plating in the electroplater's bath.

(b) Plating by dipping applies to electroplating without a battery by simple immersion. Copper is deposited on iron from a solution of copper sulphate in this way.

Synonym--Simple Immersion.

Dipping Needle. A magnet mounted in horizontal bearings at its centre of gravity. Placed in the magnetic meridian it takes the direction of the magnetic lines of force of the earth at that point. It is acted on by the vertical component of the earth's magnetism, as it has no freedom of horizontal movement. (See Magnetic Elements, and Compass, Inclination.)

Directing Magnet. In a reflecting galvanometer the magnet used for controlling the magnetic needle by establishing a field. It is mounted on the spindle of the instrument above the coil and needle.

Synonym--Controlling Magnet.

186 STANDARD ELECTRICAL DICTIONARY.

Direction. (a) The direction of an electric current is assumed to be from a positively charged electrode or terminal to a negatively charged one in the outer circuit. (See Current.)

(b) The direction of magnetic and electro-magnetic lines of force is assumed to be from north to south pole of a magnet in the outer circuit. It is sometimes called the positive direction. Their general course is shown in the cuts diagrammatically. The circles indicate a compass used in tracing their course. The magnetic needle tends to place itself in the direction of or tangential to the lines of force passing nearest it.

(c) The direction of electrostatic lines of force is assumed to be out of a positively charged and to a negatively charged surface.

Fig. 130. DIRECTION OF LINES OF FORCE OF A PERMANENT MAGNET.

Fig. 131, DIRECTION OF LINES OF FORCE OF AN ELECTRO-MAGNET.

187 STANDARD ELECTRICAL DICTIONARY.

Directive Power. In magnetism the power of maintaining itself in the plane of the magnetic meridian, possessed by the magnetic needle.

Discharge, Brush. The static discharge of electricity into or through the air may be of the brush or spark form. The brush indicates the escape of electricity in continuous flow; the spark indicates discontinuity. The conditions necessary to the production of one or the other refer to the nature of the conductor, and of other conductors in its vicinity and to the electro-motive force or potential difference; small alterations may transform one into the other. The brush resembles a luminous core whose apex touches the conductor. It is accompanied by a slight hissing noise. Its luminosity is very feeble. The negative conductor gives a smaller brush than that of the positive conductor and discharges it more readily. When electricity issues from a conductor, remote from an oppositely excited one, it gives an absolutely silent discharge, showing at the point of escape a pale blue luminosity called electric glow, or if it escapes from points it shows a star-like centre of light. It can be seen in the dark by placing a point on the excited conductor of a static-electric machine.

Synonyms--Silent Discharge--Glow Discharge.

Discharge, Conductive. A discharge of a static charge by conduction through a conductor.

Discharge, Convective. The discharge of static electricity from an excited conductor through air or rarefied gas; it is also called the quiet or silent discharge. The luminous effect in air or gas at atmospheric pressures takes the form of a little brush from a small positive electrode; the negative shows a star. The phenomena of Gassiot's cascade, the philosopher's egg and Geissler tubes, all of which may be referred to, are instances of convective discharge.

Discharge, Dead Beat. A discharge that is not oscillatory in character.

Discharge, Disruptive. A discharge of a static charge through a dielectric. It involves mechanical perforation of the dielectric, and hence the mere mechanical strength of the latter has much to do with preventing it. A disruptive discharge is often oscillatory in character; this is always the case with the discharge of a Leyden jar.

188 STANDARD ELECTRICAL DICTIONARY.

Discharge, Duration of. The problem of determining this factor has been attacked by various observers. Wheatstone with his revolving mirror found it to be 1/24000 second. Fedderson, by interposing resistance, prolonged it to 14/10000 and again to 138/10000 second. Lucas & Cazin made it from 26 to 47 millionths of a second. All these experiments were performed with Leyden jars.

Discharge, Impulsive. A disruptive discharge produced between conductors by suddenly produced potential differences. The self-induction of the conductor plays an especially important part in discharges thus produced.

Discharge, Lateral. (a) A lightning discharge, which sometimes takes place between a lightning rod and the building on which it is.

(b) In the discharge of a Leyden jar or condenser the discharge which takes the alternative path, q. v.

Discharge, Oscillatory. The sudden or disruptive discharge of a static condenser, such as a Leyden jar, or of many other charged conductors, is oscillatory in character. The direction of the currents rapidly changes, so that the discharge is really an alternating current of excessively short total duration. The discharge sends electro-magnetic waves through the ether, which are exactly analogous to those of light but of too long period to affect the eye.

Synonym--Surging Discharge.

[Transcriber's note: Marconi's transmission across the English channel occurs in 1897, five years after the publication of this book.]

Fig. 132. DISCHARGER.

Discharger. An apparatus for discharging Leyden jars. It consists of a conductor terminating in balls, and either jointed like a tongs or bent with a spring-action, so that the balls can be set at distances adapted to different sized jars. It has an insulating handle or a pair of such. In use one ball is brought near to the coating and the other to the spindle ball of the jar. When nearly or quite in contact the jar discharges.

Synonyms--Discharging Rod--Discharging Tongs.

189 STANDARD ELECTRICAL DICTIONARY.

Discharger, Universal. An apparatus for exposing substances to the static discharge spark. It consists of a base with three insulating posts. The central post carries an ivory table to support the object. The two side posts carry conducting rods, terminating in metal balls, and mounted with universal joints. A violent shock can be given to any object placed on the table.

Synonym--Henley's Universal Discharger.

Discharge, Silent. This term is sometimes applied to the glow or brush discharge and sometimes to the condition of electric effluvium. (See Discharge, Brush--Effluvium, Electric.)

Discharge, Spark. The discontinuous discharge of high tension electricity through a dielectric or into the air produces electric sparks. These are quite strongly luminous, of branching sinuous shape, and in long sparks the luminosity varies in different parts of the same spark. A sharp noise accompanies each spark. High density of charge is requisite for the formation of long sparks.

Disconnection. The separation of two parts of, or opening a circuit, as by turning a switch, unscrewing a binding screw, or the like. The term is sometimes used to indicate a class of faults in telegraph circuits. Disconnections may be total, partial or intermittent, and due to many causes, such as open or partially replaced switches, oxidized or dirty contact points, or loose joints.

Displacement, Electric. A conception of the action of charging a dielectric. The charge is all on the surface. This fact being granted, the theory of displacement holds that charging a body is the displacing of electricity, forcing it from the interior on to the surface, or vice versa, producing a positive or negative charge by displacement of electricity. While displacement is taking place in a dielectric there is assumed to be a movement or current of electricity called a displacement current.

Disruptive Tension. When the surface of a body is electrified, it tends to expand, all portions of the surface repelling each other. The film of air surrounding such a body is electrified too, and is subjected to a disruptive tension, varying in intensity with the square of the density.

Dissimulated Electricity. The electricity of a bound charge. (See Charge, Bound.)

Dissociation. The separation of a chemical compound into its elements by a sufficiently high degree of heat. All compounds are susceptible of dissociation, so that it follows that combustion is impossible at high temperatures.

190 STANDARD ELECTRICAL DICTIONARY.

Distance, Critical, of Alternative Path. The length of air gap in an alternative path whose resistance joined to the impedance of the rest of the conductors of the path just balances the impedance of the other path.

Distance, Sparking. The distance between electrodes, which a spark from a given Leyden jar or other source will pass across.

Synonym--Explosive Distance.

Distillation. The evaporation of a liquid by heat, and sometimes in a vacuum, followed by condensation of the vapors, which distil or drop from the end of the condenser. It is claimed that the process is accelerated by the liquid being electrified.

Distributing Box. In an electric conduit system, a small iron box provided for giving access to the cable for the purpose of making house and minor connections.

Synonym--Hand Hole.