Chapter I: II (3)

In the cut N S represents the poles of a powerful electro-magnet. A rectangular coil bb of wire is suspended between the coils. A stationary iron core a intensifies the field. The suspension wire f f 1 has its tension adjusted at h. This wire acts as conductor for the current.

453 STANDARD ELECTRICAL DICTIONARY.

The current is sent in one or the other direction or is cut off in practice to produce the desired oscillations of the coil b b. A glass siphon n l works upon a vertical axis l. One end l is immersed in an ink well m. Its longer end n touches a riband of paper o o. The thread k attached to one side of the coil pulls the siphon back and forth according to the direction of current going through the electro-magnet cores. A spiral spring adjusted by a hand-screw controls the siphon. In operation the siphon is drawn back and forth producing a zigzag line. The upward marks represent dots, the downward ones dashes. Thus the Telegraphic Code can be transmitted on it. To cause the ink to issue properly, electrification by a static machine has been used, when the stylus does not actually touch the paper, but the ink is ejected in a series of dots.

Fig. 286. SIPHON RECORDER.

Reducteur for Ammeter. A resistance arranged as a shunt to diminish the total current passing through an ammeter. It is analogous to a galvanometer shunt. (See Multiplying Power of Shunt.)

Reducteur for Voltmeter. A resistance coil connected in series with a Voltmeter to diminish the current passing through it. Its resistance being known in terms of the resistance of the voltmeter it increases the range of the instrument so that its readings may cover double or more than double their normal range.

Reduction of Ores, Electric. Treatment of ores by the electric furnace (see Furnace, Electric.) The ore mixed with carbon and flux is melted by the combined arc and incandescent effects of the current and the metal separates. In another type the metal is brought into a fusible compound which is electrolyzed while fused in a crucible. Finally processes in which a solution of a salt of the metal is obtained, from which the metal is obtained by electrolysis, may be included. Aluminum is the metal to whose extraction the first described processes are applied.

454 STANDARD ELECTRICAL DICTIONARY.

Refraction, Electric Double. Double refraction induced in some materials by the action of either an electrostatic, magnetic or an electro-magnetic field.

The intensity or degree of refracting power is proportional to the square of the strength of field.

Refreshing Action. In electro-therapeutics the restoration of strength or of nerve force by the use of voltaic alternatives, q. v.

Region, Extra-polar. In electro-therapeutics the area or region of the body remote from the therapeutic electrode.

Region, Polar. In electro-therapeutics the area or region of the body near the therapeutic electrode.

Register, Electric. There are various kinds of electric registers, for registering the movements of watchmen and other service. Contact or press buttons may be distributed through a factory. Each one is connected so that when the circuit is closed thereby a mark is produced by the depression of a pencil upon a sheet or disc of paper by electro-magnetic mechanism. The paper is moved by clockwork, and is graduated into hours. For each push-button a special mark may be made on the paper. The watchman is required to press the button at specified times. This indicates his movements on the paper, and acts as a time detector to show whether he has been attending to his duty.

Register, Telegraphic. A term often applied to telegraph recorders, instruments for producing on paper the characters of the Morse or other alphabet.

Regulation, Constant Current. The regulation of a dynamo so that it shall give a constant current against any resistance in the outer circuits, within practical limits. It is carried out in direct current machines generally by independent regulators embodying a controlling coil with plunger or some equivalent electro-magnetic device inserted in the main circuit and necessarily of low resistance. In some regulators the work of moving the regulator is executed mechanically, but under electrical control; in others the entire work is done by the current.

A typical regulator or governor (Golden's) of the first class comprises two driven friction wheels between which is a driving friction wheel, which can engage with one driven wheel only at once. It is brought into engagement with one or the other by a solenoid and plunger.

455 STANDARD ELECTRICAL DICTIONARY.

As it touches one wheel it turns it in one direction. This moves a sliding contact in one direction so as to increase a resistance. This corresponds to a motion of the plunger in one direction. As the driving wheel moves in the opposite direction by a reverse action it diminishes the resistance. Thus the increase and decrease of resistance correspond to opposite movements of the solenoid plunger, and consequently to opposite variations in the current. The whole is so adjusted that the variations in resistance maintain a constant amperage. The resistance is in the exciting circuit of the dynamo.

In Brush's regulator, which is purely mechanical, a series dynamo is made to give a constant current by introducing across the field magnets a shunt of variable resistance, whose resistance is changed by an electro-magnet, whose coils are in circuit with the main current. Carbon resistance discs are used which the electro-magnet by its attraction for its armature, presses with varying intensity. This alters the resistance, decreasing it as the current increases and the reverse. As the connection is in shunt this action goes to maintain a constant current.

Regulation, Constant Potential. The regulation of constant potential dynamos is executed on the same lines as that of constant current dynamos. If done by a controlling coil, it must for constant potential regulation be wound with fine wire and connected as a shunt for some part of the machine.

Regulation of Dynamos. The regulation of dynamos so that they shall maintain a constant potential difference in the leads of their circuit for multiple arc systems or shall deliver a constant current in series systems. Hence two different systems of regulation are required, (a) constant potential regulation--(b) constant current regulation. The first named is by far the more important, as it concerns multiple arc lighting, which is the system universally used for incandescent lighting.

S. P. Thompson thus summarizes the methods of governing or regulating dynamos. Premising that alteration of the magnetic flux is the almost universal way of control, it can be done in two ways; first, by varying the excitation or ampere turns of the field, and second by varying the reluctance of the magnetic circuit. The excitation or magnetic flux may be varied

(a) by hand, with the aid of rheostats and commutators in the exciting circuit;

(b) automatically, by governors, taking the place of the hand;

(c) by compound windings. The magnetic circuit may have its reluctance caused to vary in several ways;

(d) by moving the pole pieces nearer to or further from the armature;

(e) by opening or closing some gap in the magnetic circuit (field-magnet core);

(f) by drawing the armature endways from between the pole pieces;

(g) by shunting some of the magnetic lines away from the armature by a magnetic shunt.

The latter magnetic circuit methods d, e, f, and g, have never met with much success except on small machines or motors. Method e is adopted in the Edison motor, the yoke being withdrawn or brought nearer the cores of the coils. (See Regulation, Constant Current-Regulation, constant Potential.)

456 STANDARD ELECTRICAL DICTIONARY.

Reguline. adj. Having the characteristics of a piece of metal, being flexible, adherent, continuous, and coherent. Applied to electrolytic deposits.

Relative. Indicating the relation between two or more things without reference to absolute value of any one of them. Thus one lamp may be of relatively double resistance compared to another, but this states nothing of the resistance in ohms of either lamp.

Relay. A receiving instrument which moves in accordance with impulses of currents received, and in so moving opens and closes a local circuit, which circuit may include as powerful a battery as required or desirable, while the relay may be on the other hand so delicate as to work with a very weak current.

Fig. 287. RELAY.

The typical relay includes an electro-magnet and armature. To the latter an arm is attached and the lower end of the arm works in pivots. As the armature is attracted the arm swings towards the magnet. When the current is cut off, the armature and arm are drawn back by a spring. When the arm swings towards the magnet its upper end touching a contact screw closes the local circuit. When it swings back it comes in contact with a second screw, with insulated point, and opens the circuit as it leaves the first named screw.

One terminal connects with the arm through the pivots and frame. The other connects with the contact screw through the frame carrying it.

Synonym--Relay Magnet.

457 STANDARD ELECTRICAL DICTIONARY.

Relay Bells. Bells connected by relay connection to a main line for acoustic telegraphy. A stroke on one bell indicates a dot and on the other a dash. The system is now nearly extinct.

Relay, Box-sounding. A relay which is surrounded by or mounted on a resonator or wooden box of such proportions and size as to reinforce the sound. This enables a relay to act as a sounder, its weak sounds being virtually magnified so as to be audible.

Relay Connection. A connection used in telegraphy, including a local battery, with a short circuit normally open, but closed by a switch and a sounder or other appliance. The latter is made very sensitive so as to be worked by a feeble current, and is connected to the main line. A very slight current closes the switch and the local battery comes into operation to work a sounder, etc. When the current ceases on the main line the switch opens and throws the local battery out of action. The switch is termed a relay, q. v. A long main line may thus produce strong effects at distant stations, the intensity of action depending on the local battery.

Fig. 288. RELAY OR LOCAL CIRCUIT.

Relay, Differential. A relay containing two coils wound differentially, and of the same number of turns and resistance. If two equal currents pass through the coils they counteract each other and no action takes place. If there is a difference in the currents the relay acts as one coil preponderates. The coils may be wound for uneven currents with different resistance and number of turns.

Relay, Microphone. A relay connection applied to a telephone circuit. It consists of a microphone mounted in front of the diaphragm of a telephone receiver. In circuit with the microphone is a battery and second telephone receiver. The microphone is supposed to intensify the sounds of the first telephone.

458 STANDARD ELECTRICAL DICTIONARY.

Relay, Polarized. A relay whose armature is of steel, and polarized or permanently magnetized, or in which a permanent magnet is used as the basis for the electro-magnets. In the relay shown in the cut the coils shown are mounted on cores carried on the end of a powerful bent permanent magnet. Thus when no current passes their upper poles are both of the same sign, and the horizontally vibrating tongue is held by the magnetic attraction against one or the other pole piece. If a current is sent through the electro-magnet it gives opposite polarity to the two polar extensions. As the end of the vibrating tongue is of polarity determined by the permanent magnet it is attracted to one pole and repelled from the other. On cessation of current it remains attached by the permanent magnetism. If now a current is sent in the opposite direction the two poles again acquire opposite polarity, the reverse of the former, and the tongue flies across to the opposite side. On cessation of current it remains attached as before by the permanent magnetism.

In its movements to and fro the relay tongue opens and closes a contact, so as to work a sounder or other apparatus. The polarized relay is of high sensibility, and requires little or no change of adjustment.

Fig. 288. POLARIZED RELAY

Reluctance. In a magnetic circuit or portion thereof, the resistance offered to the flow of lines of force. The magnetic circuit as has already been stated is treated like an electric circuit, and in it reluctance occupies the place of resistance in the electric circuit. It is the reciprocal of permeance. S. P. Thompson expresses the law thus:

Total number of magnetic lines = (magneto-motive force) / (magnetic reluctance)

Synonyms--Magnetic Reluctance-Magnetic Resistance.

Reluctance, Unit of. The reluctance of a circuit through which unit magnetizing power (magneto-motive force) can produce a unit of induction or one line of force. This value is very high; the reluctance of ordinary magnetic circuits ranges from 1E-5 to 1E-8 unit of reluctance.

Reluctivity. Specific reluctance; the reluctance of a cube of material whose edge measures one centimeter in length. It is a quality bearing the same relation to reluctance that permeability does to permeance.

It is defined as the reciprocal of magnetic permeability. (Kenelly.) If plotted as a curve for different values of the magnetizing force it is found to be nearly a straight line, a linear function of the magnetizing force, H with the equation a + b H. Reluctivity is the property of a substance; reluctance is the property of a circuit.

459 STANDARD ELECTRICAL DICTIONARY.

Remanence. The residual magnetism left after magnetic induction, expressed in lines of force per square centimeter.

Repeater. In telegraphy an instrument for repeating the signals through a second line. It is virtually a relay which is operated by the sender, and which in turn operates the rest of the main line, being situated itself at about the middle point of the distance covered. In the simpler forms of repeater two relays are used, one for transmission in one direction the other for transmission in the other. An attendant switches one or the other in as required.

Thus a common relay is virtually a repeater for its local circuit. If such a relay is placed half way down a line, and if the line beyond it is connected as its local, it becomes a repeater.

Some forms of repeaters are automatic, and repeat both ways without the need of an attendant.

It is the practice to somewhat prolong the signals sent through a repeater.

Replenisher, Sir William Thomson's. A static accumulating influence machine contained in Thomson's quadrant electrometer and used to change the quadrants. The cut shows the horizontal section and construction of the apparatus.

It contains two gilt brass inductors A B, and two eccentric sectors or carriers, C, D, which are mounted on an ebonite spindle, which is spun around by the fingers. The springs s s1 connect each with its inductor; the springs S S1 connect only each other, and touch the sectors as they turn around.

One of the inductors may be always assumed to be of slightly higher potential than that of the other one. When the carriers are in contact with the springs S S1 they are each charged by induction with electricity opposite in sign to that of the nearest quadrant. As they leave the springs S S1 in their rotation, they next touch the springs s s1, but of the recently opposite inductor. They share each a portion of its charge with the inductors building up their charges. The action is repeated over and over again as they rotate.

Fig. 290. THOMSON'S REPLENISHER.

460 STANDARD ELECTRICAL DICTIONARY.

Reservoir, Common. A term applied to the earth, because all electrified bodies discharge into it if connected thereto.

Fig. 289. DIAGRAM OF THOMSON'S REPLENISHER.

Residual Atmosphere. The air left in a receiver after exhaustion by an air pump. The quantity, where good air pumps are used, is very minute.

Residue, Electric. The residual charge of a condenser. (See Charge, Residual.)

Resin. (a) The product obtained by non-destructive distillation of the juice of the pitch pine. It is the solid residue left after the turpentine has been evaporated or distilled. It is a mixture of abietic acid C44 H64 O5 and pinic acid C20 H30 O2. It is an insulator; its specific inductive capacity is 2.55. (Baltzmann.)

Synonyms--Colophony--Rosin.

(b) The name is also generally applied to similar substances obtained from the sap of other trees; thus shellac is a resin. The resins are a family of vegetable products; the solid portions of the sap of certain trees. Common resin, lac, dragons blood, are examples. They are all dielectrics and sources of resinous or negative electricity when rubbed with cotton, flannel, or silk. (See Electrostatic Series.)

461 STANDARD ELECTRICAL DICTIONARY.

Resinous Electricity. Negative electricity; the electricity produced upon the surface of a resinous body by rubbing it; such a body is shellac or sealing wax; flannel and other substances may be used as the rubbing material. (See Electrostatic Series.)

Resistance. (a) The quality of an electric conductor, in virtue of which it opposes the passage of an electric current, causing the disappearance of electro-motive force if a current passes through it, and converting electric energy into heat energy in the passage of a current through it. If a current passes through a conductor of uniform resistance there is a uniform fall of potential all along its length. If of uneven resistance the fall in potential varies with the resistance. (See Potential, Fall of.)

The fall of potential is thus expressed by Daniell. "In a conductor, say a wire, along which a current is steadily and uniformly passing, there is no internal accumulation of electricity, no density of internal distribution; there is, on the other hand, an unequally distributed charge of electricity on the surface of the wire, which results in a potential diminishing within the wire from one end of the wire to the other."

Resistance varies inversely with the cross section of a cylindrical or prismatic conductor, in general with the average cross-section of any conductor, and in the same sense directly with its true or average or virtual length. It varies for different substances, and for different conditions as of temperature and pressure for the same substance. A rise of temperature in metals increases the resistance, in some bad conductors a rise of temperature decreases the resistance.

462 STANDARD ELECTRICAL DICTIONARY.

Approximately, with the exception of iron and mercury, the resistance of a metallic conductor varies with the absolute temperature. This is very roughly approximate.

Except for resistance energy would not be expended in maintaining a current through a circuit. The resistance of a conductor may be supposed to have its seat and cause in the jumps from molecule to molecule, which the current has to take in going through it. If so a current confined to a molecule would, if once started, persist because there would be no resistance in a molecule. Hence on this theory the Ampérian currents (see Magnetism, Ampere's Theory of) would require no energy for their maintenance and Ampére's theory would become a possible truth.

When metals melt their resistance suddenly increases.

Light rays falling on some substances, notably selenium, q. v., vary the resistance.

Longitudinal stretching of a conductor decreases it, it increases with longitudinal compression, and increases in iron and diminishes in tin and zinc when a transverse stress tends to widen the conductor.

(b) The term resistance is used to express any object or conductor used in circuit to develop resistance.

[Transcriber's note: At room temperatures, the thermal motion of ions in the conductor's crystal lattice scatters the electrons of the current. Imperfections of the lattice contribute slightly. At low temperatures superconductivity (zero resistance) can occur because an energy gap between the electrons and the crystal lattice prevents any interaction. At the time of this book, none of this was known. "Jumps from molecule to molecule" is a good guess.]

Resistance, Apparent. Impedance; the virtual resistance of a circuit including the spurious resistance due to counter-electromotive force. It may be made up of true resistance and partly of an inductive reaction, as it represents the net factor, the entire obstruction to the passage of a current, and not merely a superadded resistance or counter-electro-motive force.

Synonym--Impedance.

[Transcriber's note: Impedance can also have a component due to capacitance.]

Resistance, Asymmetrical. Resistance which varies in amount in different directions through a conductor. It implies a compound or composite conductor such as the human system. The presence of counter-electro-motive force in different parts of a conductor may bring about asymmetrical resistance.

Resistance, B. A. Unit of. The British Association Ohm. (See Ohm, B. A.)

463 STANDARD ELECTRICAL DICTIONARY.

Resistance Box. A box filled with resistance coils. The coils are connected in series so that a circuit including any given number has their aggregate resistance added to its own. The terminals of consecutive coils are connected to short blocks of brass which are secured to the top of the box, lying flatwise upon it, nearly but not quite in contact with each other. Plugs of brass are supplied which can go in between pairs of blocks, which have a pair of grooves reamed out to receive them. Such plugs short circuit the coil below them when in position. The cut shows how such coils are connected and the use of plugs to short circuit them. The diagram shows the top of a Wheatstone bridge, q. v., resistance box with connections for determining resistances.

Fig. 291. RESISTANCE BOX.

Resistance Box, Sliding. A resistance box whose coils are set in a circle. Two metal arms with handles are pivoted at the centre of the circle and by moving them around they make and break contacts so as to throw the coils in and out of circuit. The object is to permit an operator to adjust resistance without looking at the box--an essential in duplex telegraphy.

Resistance, Breguet Unit of. The same in origin as the Digney Unit. (See Resistance, Digney Unit of.)

It is equal to 9.652 Legal Ohms.

Resistance, Carbon. A resistance, a substitute for a resistance coil; it is made of carbon, and is of various construction. In the Brush dynamo regulator a set of four vertical piles of plates of retort carbon, q. v., is used as a resistance, whose resistance is made to vary by changing the pressure. This pressure automatically increases as the current strength increases, thus reducing the resistance.

464 STANDARD ELECTRICAL DICTIONARY.

Resistance Coil, Standard. A standard or resistance issued by the Electric Standard Committee of Great Britain. The cut shows the standard ohm. It is formed either of German silver, or of an alloy of silver, 66.6 per cent. and platinum, 33.4 per cent. The wire is insulated and doubled before winding as described before. (See Coil, Resistance.) The two ends of the wire are soldered, each one to a heavy copper wire or rod r. The whole coil is enclosed in a brass case, and is enclosed with paraffine melted in at A. A place for a thermometer is provided at t. By immersing the lower part of the case B in water of different degrees of heat any desired temperature can be attained.

Fig. 292. STANDARD OHM COIL.

Resistance, Combined. The actual resistance of several parallel conductors starting from the same point and ending at the same point. If the individual resistance be a b c d .. and the combined resistance be x then we have x = 1 / (( 1/a) + (1/b) + (1/c) + (1/d) + …)

Synonym--Joint Resistance.

Resistance, Critical. In a series wound dynamo the resistance of the outer circuit above which the machine will refuse to excite itself.

Resistance, Dielectric. The mechanical resistance of a dielectric to the tendency to perforation or to the strains due to electrification. This is a phase of mechanical resistance, and is distinct from the electrical or ohmic resistance of the same substance.

Resistance, Digney Unit of. The resistance of an iron wire, 1 kilometer long, 4 millimeters diameter, temperature unknown.

It is equal to 9.163 legal ohms.

Resistance, Electrolytic. The resistance of an electrolyte to the passage of a current decomposing it. It is almost entirely due to electrolysis and is added to by counter- electro-motive force, yet it is not treated specifically as such, but as an actual resistance. When a current of a circuit of too low voltage to decompose an electrolyte is caused by way of immersed terminals to pass through an electrolyte the resistance appears very high and sometimes almost infinite. If the voltage is increased until the electrolyte is decomposed the resistance suddenly drops, and what should be termed electrolytic resistance, far lower than the true resistance, appears.

465 STANDARD ELECTRICAL DICTIONARY.

Resistance, English Absolute or Foot-Second Unit of. A unit based on the foot and second. It is equal to (( foot / second ) * 1E7) , being based on these dimensions.

It is equal to 0.30140 legal ohm.

Resistance, Equivalent. A resistance equivalent to other resistances, which may include counter-electro-motive force.

Resistance, Essential. The resistance of the generator in an electric circuit; the same as internal resistance.

Resistance, External. In an electric circuit the resistance of the circuit outside of the generator, or battery.

Synonym--Non-essential Resistance.

Fig. 293. RESISTANCE FRAME.

Resistance Frame. An open frame filled with resistance coils of iron, or German silver wire. It is used as a resistance for dynamos and the larger or working class of plant. The coils are sometimes connected so that by a switch moving over a row of studs one or more can be thrown into series according to the stud the switch is in contact with.

Resistance, German Mile Unit of. The resistance of 8,238 yards of iron wire 1/6 inch in diameter. It is equal to 56.81 legal ohms.

466 STANDARD ELECTRICAL DICTIONARY.

Resistance, Hittorf's. A high resistance, often a megohm, composed of Hittorf's solution, q. v. It is contained in a vertical glass tube near whose upper and lower ends are electrodes of metallic cadmium attached to platinum wires. The cadmium is melted in glass tubes, the platinum wire is inserted into the melted metal and the tube is broken after all is solid. The resistance should show no polarization current.

Fig. 294. HITTORF'S RESISTANCE

Resistance, Inductive. A resistance in which self-induction is present; such as a coil of insulated wire wound around an iron core.

Resistance, Insulation. The resistance of the insulation of an insulated conductor. It is stated in ohms per mile. It is determined by immersing a section of the line in water and measuring the resistance between its conductor and the water. The section must be of known length, and its ends must both be above the liquid.

Resistance, Internal. The resistance of a battery, or generator in an electric circuit as distinguished from the resistance of the rest of the circuit, or the external resistance.

Synonym--Essential Resistance.

Resistance, Jacobi's Unit of. The resistance of a certain copper wire 25 feet long and weighing 345 grains.

It is equal to 0.6296 legal ohm.

Resistance, Matthiessen's Meter-gram Standard. The resistance of a pure hard drawn copper wire of such diameter that one meter of it weighs one gram. It is equal to .1434 Legal Ohms at 0º C. (32º F.)

Resistance, Matthiessen's Unit of. The resistance of a standard mile of pure annealed copper wire 1/16 inch diameter, at a temperature of 15.5º C. (60º F.).

It is equal to 13.44 legal ohms.

467 STANDARD ELECTRICAL DICTIONARY.

Resistance, Meter-millimeter Unit of. The resistance of a wire of copper one meter long and one square millimeter in section. It is equal to .02057 ohms at 0º C. (32º F.) The term may also be applied to the resistance of similar sized wire of other metals.

Resistance, Mil-foot Unit of. The resistance of a foot of copper wire one-thousandth of an inch in diameter. It is equal to 9.831 ohms at 0º C. (32º F.) The term may also be applied to the resistance of similar sized wire of other metals.

Resistance, Non-essential. The resistance of the portion of an electric circuit not within the generator; the same as external resistance.

Synonym--External Resistance.

Resistance, Non-inductive. A resistance with comparatively little or negligible self-induction.

Resistance of Human Body. The resistance of the human body is largely a matter of perfection of the contacts between its surface and the electrodes. It has been asserted that it is affected by disease. From 350 to 8,000 ohms have been determined as resistances, but so much depends on the contacts that little value attaches to the results.

Resistance, Ohmic. True resistance measured in ohms as distinguished from counter-electro-motive force, q. v. The latter is called often spurious resistance.

Synonym--True Resistance.

[Transcriber's note: "True" vs. "spurious" are interesting terms, considering that today we define impedance as a combination of "real" resistance and "imaginary" capacitive and inductive reactance.]

Resistance, Reduced. The resistance of a conductor reduced to ohms, or to equivalent lengths of a column of mercury, 1 square millimeter in cross area.

Resistance, Siemen's Unit of. The resistance of a column of mercury 1 meter long and 1 square millimeter cross-sectional area at 0º C. (32º F.)

It is equal to .9431 legal ohm.

Resistance, Specific. The relative resistance of a substance. It is expressed as the actual resistance of a cube of the substance which is one centimeter on each edge. For metals it is usually expressed in microhms, for liquids in ohms.

The resistances of a specified length of wire of specified diameter of different substances is often given, and is really a particular way of stating specific resistances.

Synonym--Specific Conduction Resistance.

Resistance, Spurious. The counter-electro-motive force, q. v., operating to prevent a current being produced of what should be its full strength were the true resistance and actuating electro-motive force only concerned. Such counter-electro-motive force may be treated as a spurious resistance and such a value in ohms assigned to it as would correspond to its proper effect.

468 STANDARD ELECTRICAL DICTIONARY.

In its effect on opposing a current and in resisting its formation it differs from true resistance. The latter in diminishing current strength absorbs energy and develops heat; spurious resistance opposes and diminishes a current without absorption of energy or production of heat.

[Transcriber's note: "Spurious resistance" is now called reactance, consisting of capacitive reactance and inductive reactance. The combination of reactance and (Ohmic/true) resistance is called impedance. The calculation of impedance requires complex algebra, not just real values used in DC circuit analysis.]

Resistance, Steadying. When arc lamps are connected in parallel or multiple arc a small resistance coil is sometimes placed in series with each lamp for steadying purposes. It reduces the percentage of variation of resistance in each lamp, which may be caused by a change in the position of the carbons.

Resistance, Swiss Unit of. A unit constructed by the "Administration Suisse," based on the same data as the Breguet and the Digney Units. (See Resistance, Digney Unit of)

It is equal to 10.30 legal ohms.

Resistance, Thomson's Unit of. A unit of resistance based on the foot and second.

It is equal to 0.3166 legal ohm.

Resistance, Unit. Unit resistance is that of a conductor in which unit current is produced by unit electro-motive force.

Resistance, Varley's Unit of. The resistance of a standard mile of a special copper wire 1/16 inch diameter.

It is equal to 25.33 ohms.

Resistance, Weber's Absolute Unit. A metric system unit; (meter / second) * 1E7

It is equal to 0.9089 legal ohm.

Resonance, Electric. A set of phenomena known as the Hertz experiments are grouped under this title, which phenomena are incidents of and depend on the propagation of electric waves through wires or current conductors, as well as through the ether. Ordinarily a wire is only a seat of current, and is in its nature inconsistent with wave propagation through its mass. Such waves are virtually confined to the exterior of the wire. The point is that the current-producing force is supposed to enter the wire at all points from without, the current not being produced by an end-push. Hence in rapidly recurring waves which are produced by a rapidly pulsatory or alternating current, no time is afforded for the current-producing force, in this case the wave-producing force, to penetrate into the substance of the wire. In one of his experiments Dr. Hertz surrounded a wire by a glass tube chemically silvered. The coating was so thin as to be translucent. Through this metallic layer a current could be induced in the wire in its interior. Any mechanical layer of metal took up the induction itself, and protected the central wire. This gave a clue to the thickness of metal penetrated by the rapid induced waves used by Dr. Hertz.

469 STANDARD ELECTRICAL DICTIONARY.

Fig. 295. ELECTRICAL RESONANCE EXCITER.

The method used for the production of rapid oscillations is the following. To the terminals of an induction coil two metal spheres AA1 are connected as shown. This apparatus is termed the exciter; in its discharge a series of isochronous discharges takes place, alternating in direction. The period of duration T of a single one is given by the formula T= 2* PI * squareRoot( LC ), in which C is the capacity and L is the self-induction. The spheres may be 30 centimeters (11.8 inches) in diameter, connected each to conductors 0.5 centimeter (.2 inch) in diameter and 40 centimeters (15.7 inches) long each. For the length of an undulation the formula gives for this apparatus 4.8 meters (15.75 feet) as the length of a wave, assuming for them the velocity of propagation equal to that of light. The exciter may have 10,000 times the rate of oscillation possessed by the plain induction coil.

When this apparatus is worked it produces induced waves in every neighboring conductor. The resonance effects appear in the size of the spark induced. Thus a wire bent into a circle with its ends nearly touching will give a spark, but if made of proper electrostatic capacity, corresponding with the particular waves employed, the spark will be very much larger. The ring, with its spark gap is termed a resonator. It is used as an explorer to trace the waves.

Waves thus produced are transmitted by stone walls and nonconductors in general. A plate of zinc reflects part and transmits part. The reflected waves can be traced by the resonator, their angle of reflection being equal to their angle of incidence. They can be received by one parabolic reflector, reflected to another and brought to a focus. They can be reflected so as to produce interference or loops and nodes, and the loops and nodes can be traced by the resonator. By a prism of asphalt they are refracted exactly like light.

From all this it is concluded that an additional proof is furnished of the identity of light and electro-magnetic waves, and a very strong experimental proof of Maxwell's theory of light is furnished.

Synonym--Hertz's Experiments.

470 STANDARD ELECTRICAL DICTIONARY.

Fig. 296. ELECTRICAL RESONATOR.

Resonator, Electric. A small open electric circuit, with ends nearly touching. When exposed to electric resonance, or to a sympathetic electric oscillatory discharge, a spark passes from across the gap. The production of this spark is altogether a matter of the inductance of the resonator. The simplest form is a circle of copper wire with its ends nearly touching. The length of the gap is adjustable by bending. A screw adjustment may also be provided. Another form is shown in the cut, Fig. 296. Here sheets of tinfoil are used to regulate the electrostatic capacity, while at m is shown the finger piece for regulating the size of the spark gap a.

Synonym--Spark Micrometer.

Resultant. The line indicating the result of the application of two or more forces to a point. Its direction and length give the elements of direction and intensity. (See Forces, Resolution of Forces, Composition of Components.)

Resultant Polarity. The magnetic polarity imparted to a mass of iron acted on by two or more separate inducing forces or currents. It appears in dynamos and motors. The final polarity is the resultant of the inducing effect of the field magnet poles and of the windings.

Retardation. In telegraphy a retardation of the rate of transmission of signals. It is due to several causes.

(a) The self-induction of the circuit, especially if it includes many electro-magnets, produces extra currents (see Currents, Extra.) These are opposed to the main current on closing it and hence retard the action. They are in the same direction on opening it and hence again retard the action.

(b) Every line has a certain static capacity. This is affected by the proximity of the lines to the earth. For each signal electricity has to be charged upon the line until the line is charged to its end with a certain proportion of the initial density. This charging takes time and hence introduces retardation.

(c) The cores of the electro-magnets of the relays or sounders are not instantly magnetized and demagnetized. This magnetic lag, q. v., introduces retardation.

471 STANDARD ELECTRICAL DICTIONARY.

Retardation of Phase. The fractional lagging behind of waves or alternating currents; by lagging behind a portion of a wave length the corresponding phases, as of full amplitude, are kept back or retarded. The phase of current intensity may be retarded with reference to the electro-motive force by the introduction of transformers of high capacity with high resistance on open secondary circuits.

[Transcriber's note: Capacitors are used to correct current phase lag.]

Retentivity. Coercitive or coercive force; by virtue of which steel retains its magnetism. It is the more modern name, "coercive force" as a term being rejected by many.

Synonyms--Coercive Force--Coercitive Force.

Retort Carbon. Carbon deposited in coal gas retorts from decomposition of the hydrocarbons. It is a very hard, pure form, and is of graphitic modification. Owing to its great hardness it is little used for electrical purposes, the molded carbons being easier to make. The deposition occurs in the regular gas-making process, and is a disadvantage to the working.

Return. A line or conductor which is supposed to carry current back to its starting point, after it has traversed a line. It may be a wire or the grounding of the ends of a line [or] may make the earth act as a return, termed ground- or earth-return. The best distinction of a return is to so term the portion of a circuit on which no apparatus is placed.

Reversibility. The principal in virtue of which a device for producing a given form of energy can absorb the same and do work. The reversibility of the dynamo is its quality in virtue of which it can act as a current generator, thereby converting mechanical energy into electric energy, or if a current is passed through it, it rotates, doing work, and thereby converting electric energy into mechanical energy. The knowledge of this principle can be traced back to Jacobi in 1850.

Reversible Bridge. A form of Wheatstone's Bridge adapted for reversal of the positions or interchange of the proportionate arms, v., so that the accuracy of the coils can be tested.

Rheochord. An apparatus by means of which variable quantities of wire are thrown into the circuit; a rheostat using wire. (See Rheostat, Wheatstone's.)

Rheometer. A galvanometer. (Obsolete.)

472 STANDARD ELECTRICAL DICTIONARY.

Rheomotor. A source of current; a current generator; a producer of potential difference. (Obsolete.)

Rheophore. The portion of an active circuit capable of deflecting a magnetic needle. This properly includes all of the metallic conductor of a circuit. (Obsolete.)

Rheoscope. A galvanoscope; an instrument for qualitatively detecting potential difference, fall or rise. (See Galvanoscope.)

Rheostat. An adjustable resistance; an apparatus for changing the resistance without opening the circuit. Its action may depend on the introduction of variable lengths of mercury column, of some other liquid, or of wire into a circuit. (See Rheostat, Wheatstone's.)

Rheostat Arm. The third arm of known resistance in a Wheatstone bridge. (See Proportionate Arms.)

Rheostatic Machine. An apparatus for increasing potential difference. It consists of a number of static condensers. They are charged in multiple arc or in parallel, and are discharged in series. Secondary batteries may be used for the charging; thus a static effect is produced from a galvanic battery.

Rheostat, Wheatstone's. This apparatus consists of two cylinders, one, A, made of brass, the other, B, of wood, with a spiral groove. At its end is a copper ring a. A fine brass wire has one end attached to this ring. Its other end is fastened at e, and it is wound as shown; n and o are binding screws connected, one with the cylinder-ring a, the other with the brass cylinder, A. The current entering at o, traverses the wire on B, as there the windings are insulated by the grooves, thence it passes to m and by A, whose metal short circuits all the wire on it, to the binding-post n. The handle, d, is turned one way or the other to regulate the length of the wire through which the current must pass. On each cylinder there is a square head, one of which is shown at c, so that the handle can be shifted from one to the other as required; to A if the wire is to be wound on that cylinder, to B if the reverse is desired.

Fig. 297. WHEATSTONE'S RHEOSTAT.

473 STANDARD ELECTRICAL DICTIONARY.

Rheotome. An automatic circuit breaker, one which rapidly opens and closes a circuit, as in the case of the primary of an induction coil an interrupter. (Obsolete.)

Rheotrope. A pole changer, current reverser, or commutator, g., such as the commutator of an induction coil. (Obsolete.)

Rhigolene. A petroleum product; a hydrocarbon of low boiling point. Its vapor is used in flashing (q. v.) carbon filaments for incandescent lamps.

Rhumbs. In a mariners' compass, the thirty-two points, designated, north, north by east, north north east, etc. (See Compass Mariner's-Compass, Points of the.)

Rhumkorff Coil. The induction coil, q. v.

Rigidity, Molecular. The tendency of molecules to resist rotation or change of position; the assumed cause of magnetic coercive force, or retentivity.

Ring Contact. A contact formed by a terminal clip in the shape of a ring, split or cut at one point so that its ends tend to spring together. The other terminal is a bar which passes into the cut and is tightly pressed by the elastic ring.

Fig. 298. SWITCH WITH RING CONTACTS.

474 STANDARD ELECTRICAL DICTIONARY.

Ring, Faraday. A closed ring of iron used as the core of a transformer or induction coil. The term is derived from Faraday's classic experiment with such an apparatus when he produced a spark by induction in a secondary circuit.

Roaring. A term applied to the noise sometimes produced in a voltaic arc, when the electrodes are close together and a heavy current is passing.

Rocker. In a dynamo the movable piece, mounted concentrically with the commutator, and carrying the rocker-arms and brush-holders. By moving it the brushes are adjusted for proper lead.

Rocker Arms. The arms projecting from a rocker and each carrying one of the brush-holders.

Roget's Spiral. An experimental apparatus for illustrating the mutual attraction of currents going in like direction. A cylindrical helix or spiral of wire is suspended by one end. Its lower end just dips into a mercury cup. An active circuit is connected, one terminal to the upper end, the other terminal to the mercury cup, bringing the apparatus in series into the circuit. The current as it passes causes the coil to shorten, each spiral attracting its neighbors. This breaks the circuit by drawing the lower end out of the mercury cup. The current being cut off the coils cease to attract each other, and the end dips into the mercury cup again. This closes the circuit, the coils again attract each other and the same sequence follows and is repeated over and over again. A bright spark is produced at each break of the mercury contact.

Rotation of Liquids, Electro-dynamic. By passing a current through a liquid, such as dilute sulphuric acid, it rotates if exposed to the induction of a current flowing at right angles to it. The condition resolves itself into a liquid traversed by horizontal currents from centre to circumference or vice versa, rotated by a current passing through a circular conductor below it.

475 STANDARD ELECTRICAL DICTIONARY.

Rotation of Liquids, Electro-magnetic. The rotation produced in a liquid carrying centripetal or centrifugal currents by an electromagnet. It is practically an intensification of electro-dynamic rotation. (See Rotation of Liquids, Electro-dynamic.)

Rubber. In a frictional electric machine the cushion of leather which is pressed against the plate as it rotates.

S. (a) Symbol for second.

(b) Symbol for space, or length; L is preferable.

(c) Symbol for south-seeking pole of a magnet.

Saddle Bracket. A bracket carried on the top of telegraph poles, carrying an insulator for the upper wire.

Safety Device. (a) A device to prevent overheating of any portion of a circuit by excess of current. It generally consists of a slip of fusible metal which if the current attains too much strength melts and opens the circuit. To ensure its breaking a weight is sometimes suspended from the strip. In one form an insulated German silver wire is wrapped around the end of the fusible strip a number of times and its end is connected to it. The other end of the German silver wire connects with the main lead, so that all the current goes through both in series. If the German silver wire becomes heated from excess of current the coil wrapped tightly around the end of the fusible strip melts it and opens the circuit.

(b) Lightning arresters, q. v., may be cited under this heading.

Synonyms--Automatic Cut Out--Safety Fuse, Plug, or Strip.

Fig. 299. COCKBURN SAFETY FUSE.

Safety Fuse. A strip of metal inserted so as to form part of a circuit and of such size that a smaller current [than] would heat the regular wire of the circuit dangerously, so as to cause a conflagration for instance, would melt the fuse and open the circuit. As it sometimes happens that a safety fuse melts without parting a weight is sometimes hung upon it, so as to break it as it softens.

Salt. A salt is a chemical compound containing two atoms of two radicals,. which saturate each other. One atom or radical is electro-positive referred to the other, which is electro-negative. By electrolysis salts are decomposed, the atoms or radicals separating and uniting to form new molecules.

476 STANDARD ELECTRICAL DICTIONARY.

Saturated. adj. A liquid is saturated with a substance when it has dissolved all that it can, while an excess is present in the liquid. It is possible, by dissolving some salts in hot water and allowing the solution to cool without access of air, to obtain a supersaturated solution. On introduction of a crystal of the salt, or often on mere access of air, the solution forms crystals and the liquid left is saturated.

Saw, Electric. A platinum coated steel wire mounted and connected to be raised to incandescence for cutting purposes.

Schweigger's Multiplier. An old term for the galvanometer as invented by Schweigger soon after Oerstedt's discovery.

Scratch Brushes. Brushes for cleaning the surface of articles to be electroplated to give a good metallic surface suitable for deposition. They have often wire instead of bristles.

477 STANDARD ELECTRICAL DICTIONARY.

Fig. 300. WIRE GAUZE ELECTRIC SCREEN.

Screen, Electric. A large plate or a hollow case or cage of conducting material connected with the earth, and used to protect any body placed within it from electrostatic influences.

If within a hollow conducting sphere an electrified body is placed, the inner surface of the sphere will be charged with electricity of opposite kind to that of the sphere, and the outer surface with the same kind as that of the sphere. Thus the sum of the electricities called into action by induction is zero. The two inner charges are bound to each other. The induced charge on the outer surface of the sphere is all that has any effect on objects in the outer air.

If the outer surface is connected to the earth it becomes discharged, and however highly electrified the body introduced into the sphere and the inner surface of such sphere may be, they produce no external effects, as they are bound one to the other.

If the sphere is connected to the earth and an unelectrified object is placed within it, such object will be perfectly shielded from the effects of an outer electrostatic field. Perforated tinfoil or wire gauze has just as good a result. A large plate of metal connected to the earth has the same effect. The screen whether plane or hollow simply retains a bound charge due to the field of force, thereby neutralizing it, and the electricity of the opposite sign escapes to the earth. Thus a true shielding or screening effect is produced.

In the cut an experiment is shown in which an electric screen is carried by a Leyden jar. Pith balls are suspended outside and inside of it. By the approach of an electrified body the outer pith balls will diverge, while no effect is produced upon the inner ones.

Secondary Actions. In electrolysis the direct products of the electrical decomposition are not always obtained at the electrodes, but products due to their reaction on the water and other chemicals may appear. These constitute secondary actions. Thus if a solution of copper sulphate is electrolyzed with platinum electrodes, metallic copper appears at one pole and sulphuric acid and oxygen gas at the other. But the products of electrolysis by the current are copper (Cu) and sulphion (SO4). The latter reacting on water sets free oxygen gas and forms sulphuric acid. The latter is a secondary action.

Secondary Generator. (a) An alternating current converter generating a so-called secondary current.

(b) A secondary battery, q. v., may be thus termed.

Secondary, Movable. The term movable secondaries has been applied to rings, spheres and discs of conducting material, such as copper, whose behavior when near the pole of an electro-magnet traversed by an alternating current, have been studied by Elihu Thomson. Such masses are subjected to very peculiar movements and mutual reactions. As the phenomena are due to induced currents the above term has been applied to the masses in which the currents are induced.

478 STANDARD ELECTRICAL DICTIONARY.

Secondary Plates, Colors of. In a secondary battery of the lead plate type, the color of the plates is a good indication of the condition of the battery. The negative plate should be brown or deep-reddish, the other should be slate-colored.

Secondary Poles. Poles sometimes found in magnets existing in positions intermediate between the end or true poles.

Synonym--Consequent Poles.

Seebeck Effect. The production of a current by heating the junction of two different metals forming part of a circuit, or the thermo-electric production of current, is stated as the Seebeck effect, having been discovered by that investigator.

Selenium. A non-metallic element. It is interesting electrically on account of the changes its electric resistance undergoes when it is subjected to light.

In one set of experiments it was found that diffused light caused the resistance to fall in the ratio of 11 to 9. Full sunlight reduced it to one-half. Of the spectrum colors red was most powerful and the ultra red region still more strongly affected its resistance.

The effect produced by exposure to light is instantaneous, but on removal to the dark only slowly disappears.

A vessel of hot water was found to have no effect, showing that short ether waves are essential to the effect.

Selenium Cell. A selenium resistance box. Vitreous selenium is made by keeping ordinary selenium for some hours at a temperature of about 220º C. (428º F.) after fusing. It is placed in an electric circuit as part of the conductor.

Its resistance can then be determined. It decreases in sunlight to about one-half its resistance in the dark.

The selenium cell is used in the Photophone, q. v. Otherwise it is little more than a subject of experiment.

Selenium Eye. A model eye in which selenium in circuit with a battery and galvanometer takes the place of the retina of the human eye.

Self-repulsion. When a body is electrified each molecule repels its neighbor and the condition in question is thus designated. An electrified soap-bubble expands in virtue of self-repulsion.

Semi-conductors. Substances which conduct static electricity poorly, but quite appreciably and beyond the extent of leakage. The following are examples: Alcohol and ether, powdered glass, flowers of sulphur, dry wood, paper, ice at 0º C. (32º F.)

479 STANDARD ELECTRICAL DICTIONARY.

Sensibility. The measure of the effect of a current upon a galvanometer, or any similar case.

Sensitiveness, Angle of Maximum. Every galvanometer has its angle of maximum sensitiveness, which is the angle of deflection at which a small increment of current will produce the greatest deflection. For every tangent galvanometer 45° is the angle in question. In using a galvanometer for direct reading methods it is an object to have it work at its angle of maximum sensitiveness.

Separately Excited Dynamo. A dynamo-electric machine whose field magnet is excited from an outside source, which may be another dynamo or a battery. Alternating current dynamos are often of this description.