Chapter I: II (4)

Separate Touch. In magnetism a method of inducing magnetism in a steel bar. The opposite poles of two magnets are applied at the center of the bar to be magnetized, but without touching each other, and are drawn apart to its ends. They are returned through the air and the process is repeated a number of times and on both sides of the bar if necessary.

Separation of Electricities. Under the double fluid theory of electricity the action of electrification in accumulating positive electricity in one conductor and negative on the other of the excited surfaces of two conductors.

Separator. India rubber bands or other forms used in batteries to keep the plates from touching in the cell; especially applied to secondary batteries, where the plates are so near together as to require separators to prevent short circuiting.

Fig. 301. SERIES CONNECTION.

Series. (a) Arranged in succession as opposed to parallel. Thus if a set of battery jars are arranged with the zinc of one connected to the carbon of the next one for the entire number, it is said to be arranged in series. When incandescent lamps are arranged in succession so that the current goes through one after the other they are arranged in series.

The opposite of parallel, q. v., or multiple arc, q. v.; it may be used as a noun or as an adjective.

(b) See Electro-Chemical Series;

(c) Thermo-Electric Series

(d) Electrostatic Series;

(e) Electro-motive Series.

Synonym--Cascade Connection (but little used.)

480 STANDARD ELECTRICAL DICTIONARY.

Series-multiple. Arrangement of electric apparatus, in which the parts are grouped in sets in parallel and these sets are connected in series. It is used as a noun, as "arranged in series-multiple," or as an adjective, as "a series-multiple circuit or system."

Fig. 302. SERIES-MULTIPLE CONNECTION.

Service Conductors. In electric distribution the equivalents of service pipes in the distribution of gas; wires leading from the street mains to the houses, where current is to be supplied.

Serving. The wrapping or winding of a cable composed of small size wire, laid closely and smoothly with a tool called a serving mallet, or serving block, or by machinery. It serves to protect the cable from wear.

Shackle. In telegraph lines a swinging insulator bracket for use where wires make an angle with the pole. A journal box is attached to the pole, like half of a gate hinge. To this a short iron arm is pivoted so as to be free to swing through a considerable angle. At its end an insulator is carried to which the wire is attached. The shackle swings into line with the wire, or takes a position for two wires corresponding to the resultant of their directions of pull.

Fig. 303. DOUBLE SHACKLE

Shadow. Electric. A term applied to a phenomenon of high vacua. If an electric discharge is maintained in a Crookes' tube the glass opposite the negative electrode tends to phosphoresce. A plate of aluminum, used also as the positive electrode, protects the glass directly behind it so as to produce the effect of a shadow.

Synonym--Molecular Shadow.

[Transcriber's note: The effect is due to the "shadowing" of the electrons streaming past the plate.]

481 STANDARD ELECTRICAL DICTIONARY.

Sheath for Magnet Coils. In 1867 C. E. Varley proposed the use of a copper sheath surrounding a magnet core to diminish self-induction. It has since been used by Brush and others. Sometimes metallic foil is laid between the successive coils of wire.

Synonym--Mutual Induction Protector.

Sheath for Transformers. A protective sheath of copper, interposed between the primary and secondary circuits of an alternating current transformer. It is connected to the earth. If the primary coil loses its insulation before it can leak to the secondary it is grounded. This protects the secondary circuit from the high electro-motive force of the primary circuit.

Shellac. A resin; produced as an exudation upon the branches of certain Asiatic trees, such as the banyan (Ficus religiosa). It is due to punctures in the bark of the trees in question, which punctures are made by the female of the insect coccus ficus or c. lacca.

Commercial shellac contains about 90 per cent. of resinous material, the rest is made up of wax, gluten, coloring matter and other substances.

Shellac is soluble in alcohol, and in aqueous solutions of ammonium chloride, of borax and in strong ammonia solution. Long standing is required in the case of the last named solvent. Dilute hydrochloric and acetic acids dissolve it readily; nitric acid slowly; strong sulphuric acid is without action on it. Alkalies dissolve it.

In electric work it is used as an insulator and dielectric. Its alcoholic solution is used to varnish glass plates of influence machines, for the coils of induction coils and similar purposes.

Resistance in ohms per centimeter cube at 28° C. (82.4 F.)--(Ayrton), 9.0E15

Specific Inductive Capacity (Wüllner), 2.95 to 3.73

The same substance in less pure forms occurs in commerce, as stick lac, lump lac, seed lac, button lac.

Shellac Varnish. Solution of shellac in alcohol; methylic alcohol (wood alcohol or wood naphtha) is often used as solvent.

Dr. Muirhead recommends button lac, dissolved in absolute alcohol, and the top layers decanted. For highest insulation he dissolves the lac in ordinary alcohol, precipitates by dropping into water, collects the precipitate, dries and dissolves in absolute alcohol.

Shielded. adj. An electric measuring instrument of the galvanometer type is shielded when it is so constructed that its indications are not seriously affected by the presence of neighboring magnets or by fields of force. Shielding can be effected by using a very strong permanent magnet to produce a field within which the magnetic needle moves and which reacts upon it, or by enclosing the instrument in a thick iron box.

482 STANDARD ELECTRICAL DICTIONARY.

S. H. M. Symbol or abbreviation for "simple harmonic motion."

Shock, Break. A term in electro-therapeutics; the shock received when an electric circuit, including the patient in series, is broken or opened.

Synonym--Opening Shock.

Shock, Electric. The effect upon the animal system of the discharge through it of electricity with high potential difference. Pain, nervous shock, violent muscular contortions accompany it. Of currents, an alternating current is reputed worse than a direct current; intermediate is the pulsatory current.

The voltage is the main element of shock, amperage has also some direct influence.

Shock, Static. A term in electro-therapeutics. The application of static discharges from small condensers or Leyden jars to a patient who is insulated from the ground with one electrode applied to the conducting surface on which he rests, while the other, a spherical electrode, is brought near the body so as to produce a disruptive or spark discharge.

Short Circuit. A connection between two parts of a circuit, which connection is of low resistance compared to the intercepted portion. The term is used also as a verb, as "to short circuit a lamp."

Fig. 304. DIAGRAM ILLUSTRATING SHORT CIRCUIT WORKING.

Short Circuit Working. A method of working intermittently an electro-magnet so as to avoid sparking. It consists in providing a short circuit in parallel with the magnetic coils. This short circuit is of very low resistance. To throw the magnet into action the short circuit is opened; to throw it out of action the short circuit is closed. The shunt or short circuit must be of negligibly small resistance and inductance.

483 STANDARD ELECTRICAL DICTIONARY.

Shovel Electrodes. Large plate electrodes used in a medical bipolar bath. (See Bath, Bipolar.)

Shunt. In a current circuit a connection in parallel with a portion of the circuit. Thus in a dynamo a special winding for the field may have its ends connected to the bushes, from which the regular external circuit also starts. The field is then wound in shunt with the armature. In the case of a galvanometer a resistance coil may be put in parallel with it to prevent too much current going through the galvanometer; this connection is a shunt.

The word is used as a noun, as "a shunt," or "a connection or apparatus in shunt with another," and as an adjective, as "a shunt connection," or as a verb, as "to shunt a battery."

Shunt Box. A resistance box designed for use as a galvanometer shunt. (See Shunt, Galvanometer.) The box contains a series of resistance coils which can be plugged in or out as required.

Shunt, Electro-magnetic. In telegraphy a shunt for the receiving relay consisting of the coils of an electro-magnet. It is placed in parallel with the relay. Its poles are permanently connected by an armature. Thus it has high self-induction.

On opening and closing the circuit by the sending key, extra currents are produced in the shunt. The connections are so arranged that on making the circuit the extra current goes through the relay in the same direction as the principal current, while on breaking the circuit the induced current goes in the opposite direction.

Thus the extra currents accelerate the production and also the cessation of signalling currents, tending to facilitate the operations of sending despatches.

Shunt, Galvanometer. A resistance placed in parallel with a galvanometer, so as to short circuit its coils and prevent enough current passing through it to injure it. By knowing the resistance of the shunt and of the galvanometer coils, the proportion of current affecting the galvanometer is known. This gives the requisite factor for calculation. (See Multiplying Power of Shunt.)

Shunt Ratio. The coefficient expressing the ratio existing between the current in a shunt and in the apparatus or conductor in parallel with it. (See Multiplying Power of/ Shunt.)

Shunt Winding. A dynamo or motor is shunt-wound when the field magnet winding is in shunt or in parallel with the winding of the armature.

Shuttle Current. A current alternating in direction; an alternating current.

484 STANDARD ELECTRICAL DICTIONARY.

Side-Flash. A bright flashing lateral discharge from a conductor conveying a current due to a static discharge.

Sighted Position. In an absolute electrometer (see Electrometer, Absolute) the position of the balanced arm carrying the movable disc or plate, when the disc and guard plate are in one plane. The cross-hair on the lever-end is then seen midway between two stops, or some other equivalent position is reached which is discerned by sighting through a magnifying glass or telescope.

Silver.
A metal; one of the elements; symbol Ag.; atomic weight, 108; valency, 1;
equivalent, 108; specific gravity, 10.5. It is a conductor of electricity.
Relative resistance, annealed, 1.0
Specific Resistance, annealed, at 0° C. (32° F.) 1.504 microhms.
Resistance of a wire at 0° C. (32° F.), Annealed. Hard Drawn.
(a) 1 foot long, weighing 1 grain, .2190 ohms .2389 ohms.
(b) 1 foot long, 1/1000 inch thick, 9.048 " 9.826 "
(c) 1 meter long, weighing 1 gram, .1527 " .1662 "
(d) 1 meter long, 1 millimeter thick, .01916 " .02080 "

Resistance annealed of a 1-inch cube, at 0° C. (32°F.) .5921 microhms.

Percentage increase in resistance per degree C.
(1.8 F.) at about 20° C. (68° F.), annealed, 0.377 per cent.

Electro-chemical equivalent, (Hydrogen = .0105) .1134 mgs.

Silver Bath. A solution of a salt of silver for deposition in the electroplating process.

The following is a typical formula:
Water, 10.0 parts by weight.
Potassium Cyanide, 5 " "
Metallic Silver, 2.5 " "

The silver is first dissolved as nitrate and converted into cyanide and added in that form, or for 2.5 parts metallic silver we may read: Silver cyanide, 3 parts by weight.

While many other formulas have been published the above is representative of the majority. Other solvents for the silver than potassium cyanide have been suggested, such as sodium hyposulphite, but the cyanide solution remains the standard.

Silver Stripping Bath. Various baths are used to remove silver from old electroplated articles. Their composition depends upon the base on which the metal is deposited. Silvered iron articles are placed as anodes in a solution of 1 part potassium cyanide in 20 parts of water. As kathode a silver anode or a copper one lightly oiled may be used. From the latter the silver easily rubs off. For copper articles a mixture of fuming sulphuric acid and nitric acid (40º Beaumé) may be used. The presence of any water in this mixture will bring about the solution of the copper. Or fuming sulphuric acid may be heated to between 300º and 400º F., some pinches of dry pulverized potassium nitrate may be thrown in and the articles at once dipped. These methods effect the solution of the silver, leaving the copper unattacked.

485 STANDARD ELECTRICAL DICTIONARY.

Simple Substitution. A method of obtaining a resistance equal to that of a standard. The standard is put in circuit with a galvanometer and the deflection is noted. For the standard another wire is substituted and its length altered until the same deflection is produced. The two resistances are then evidently identical. The standard can be again substituted to confirm the result.

Sine Curve. If we imagine a point moved back and forth synchronously with a pendulum, and if such point made a mark upon paper, it would trace the same line over and over again. If now the paper were drawn steadily along at right angles to the line of motion of the point, then the point would trace upon it a line like the profile of a wave. Such line is a sine curve. It derives its name from the following construction. Let a straight line be drawn, and laid off in fractions, such as degrees, of the perimeter of a circle of given diameter. Then on each division of the line let a perpendicular be erected equal in height to the sine of the angle of the circle corresponding to that division; then if the extremities of such lines be united by a curve such curve will be a sine curve.

In such a curve the abscissas are proportional to the times, while the ordinates are proportional to the sines of angles, which angles are themselves proportional to the times. The ordinates pass through positive and negative values alternately, while the abscissas are always positive.

Any number of sine curves can be constructed by varying the diameter of the original circle, or by giving to the abscissas a value which is a multiple of the true length of the divisions of circle. If the pendulum method of construction were used this would be attained by giving a greater or less velocity to the paper as drawn under the pendulum.

A species of equation for the curve is given as follows: y = sin( x )

In this x really indicates the arc whose length is x, and reference should be made to the value of the radius of the circle from which the curve is described. It will also be noticed that the equation only covers the case in which the true divisions of the circle are laid off on the line. If a multiple of such divisions are used, say n times, or 1-n times, then the equation should read y = n sin( x ) or y = sin( x ) / n

Synonyms--Curve of Sines--Sinusoidal Curve--Harmonic Curve.

486 STANDARD ELECTRICAL DICTIONARY.

Sine Law. The force acting on a body is directly proportional to the sine of the angle of deflection when--

I. The controlling force is constant in magnitude and direction; and

II. The deflecting force, although variable in its direction in space, is fixed in direction relatively to the deflecting body.

Single Fluid Theory. A theory of electricity. Electricity, as has been said, being conveniently treated as a fluid or fluids, the single fluid theory attributes electrical phenomena to the presence or absence of a single fluid. The fluid repels itself but attracts matter; an excess creates positive, a deficiency, negative electrification; friction, contact action or other generating cause altering the distribution creates potential difference or electrification. The assumed direction (see Direction) of the current and of lines of force are based on the single fluid theory. Like the double fluid theory, q. v., it is merely a convenience and not the expression of a truth. (See Fluid, Electric, and Double Fluid Theory.)

Synonym--Franklin's Theory.

Single Fluid Voltaic Cell. A galvanic couple using only a single fluid, such as the Smee or Volta cell.

Simple Harmonic Motion. Motion of a point or body back and forth along a line; the motion of a pendulum, as regards its successive swings back and forth, is an example of harmonic motion.

Sinistrotorsal. adj. The reverse of dextrotorsal, q. v. A helix with left-handed winding, the reverse of an ordinary screw, such as a wood-screw or corkscrew.

Skin Effect. A current of very brief duration does not penetrate the mass of a conductor. Alternating currents for this reason are mainly conducted by the outer layers of a conductor. The above is sometimes called the skin effect.

Sled. A contact for electric cars of the conduit system. It is identical with the plow, q.v., but is drawn after the cars instead of being pushed along with them.

Slide Meter Bridge. A name for a Slide Bridge one meter long. There are also slide half meter and slide quarter meter bridges and others. (See Meter Bridge.)

S. N. Code. Abbreviation for single needle code, the telegraphic alphabet used with the single needle system.

Soaking-in-and-out. A term for the phenomena of the residual electrostatic charge; the gradual acquirement or loss by a condenser of a portion of its electrostatic charge.

487 STANDARD ELECTRICAL DICTIONARY.

Soldering, Electric. (a) Soldering in which the solder is melted by means of electricity; either current incandescence or the voltaic arc may be used. It is identical in general with electric welding. (See Welding, Electric.)

(b) The deposition by electric plating of a metal over the ends of two conductors held in contact. This secures them as if by soldering. It is used in connecting the carbon filament of an incandescent lamp with the platinum wires that pass through the glass. Copper is the metal usually deposited.

Solenoid. The ideal solenoid is a system of circular currents of uniform direction, equal, parallel, of equal diameter of circle, and with their centers lying on the same straight line, which line is perpendicular to their planes.

Fig. 305. EXPERIMENTAL SOLENOID.

The simple solenoid as constructed of wire, is a helical coil, of uniform diameter, so as to represent a cylinder. After completing the coil one end of the wire is bent back and carried through the centre of the coil, bringing thus both ends out at the same end. The object of doing this is to cause this straight return member to neutralize the longitudinal component of the helical turns. This it does approximately so as to cause the solenoid for its practical action to correspond with the ideal solenoid.

Instead of carrying one end of the wire through the centre of the coil as just described, both ends may be bent back and brought together at the centre.

A solenoid should always have this neutralization of the longitudinal component of the helices provided for; otherwise it is not a true solenoid.

Solenoids are used in experiments to represent magnets and to study and illustrate their laws. When a current goes through them they acquire polarity, attract iron, develop lines of force and act in general like magnets.

A solenoid is also defined as a coil of insulated wire whose length is not small as compared with its diameter.

488 STANDARD ELECTRICAL DICTIONARY.

Sonometer, Hughes'. A sound measurer; a modification of a portion of Hughes' induction balance, used for testing the delicacy of the ear or for determining the relative intensity of sounds. (See Hughes' Induction Balance.) It is the arrangement of three coils, two mounted one at each of the ends of a graduated bar, and the third one between them and free to slide back and forth thereon.

Sonorescence. The property of producing sounds under the influence of momentary light radiations rapidly succeeding each other. It is the property utilized in the photophone, q. v.

Fig. 306. MORSE SOUNDER.

Sounder. In telegraphy an instrument consisting of an electromagnet with armature attached to an oscillating bar, the range of whose movements is restricted by adjusting screws. The armature is drawn away from the magnet by a spring. When a current is sent through the magnet the armature is drawn towards the poles and produces a sound as the bar strikes a striking piece or second adjusting screw. When the current ceases the bar and armature are drawn back, striking the first mentioned screw with a distinct sound, the back stroke.

The sounder is used to receive Morse and analogous character messages. The forward strokes correspond to the beginnings of the dots or dashes of the code, the back strokes to beginnings of the intervals. The distinction between dots and dashes is made by observing the interval between forward and back stroke.

Various devices are used to increase the sound. Sometimes a resonance box is used on which the sounder is mounted.

In practice sounders are generally placed on local circuits and are actuated by relays.

489 STANDARD ELECTRICAL DICTIONARY.

Sound Reading. The art or method of receiving telegraph messages by ear. It is now universally used by all expert Morse operators. It can only be applied to telegraph systems producing audible sounds; in some cases, as in needle telegraphy, it may be quite inapplicable.

Space, Clearance. The space between faces of the pole pieces and the surface of the armature in a dynamo. It is really the air gap, but in calculating dynamo dimensions the thickness of the insulated copper wire windings of the commutator are counted in as part of the air gap, because copper is almost the same as air in impermeability. Clearance space is a mechanical factor; the air gap is an electric or magnetic factor.

Synonym--Inter-air Space.

Space, Crookes' Dark. In an exhausted tube, through which an electric discharge is caused to pass, the space surrounding the negative electrode of the tube. This space is free from any luminous effect, and by contrast with the light of the discharge appears dark. The vacuum may be made so high that the dark space fills the whole space between the electrodes. It is less for a less vacuum and varies for other factors, such as the temperature of the negative electrode from which it originates, the kind of residual gas present, and the quality of the spark.

Space, Faraday's Dark. The space in an exhausted tube between the luminous glows about the two electrodes.

Space, Interferric. A term for the air-gap in a magnetic circuit. It is etymologically more correct than air-gap, for the latter is often two-thirds or more filled with the insulating material and copper wire of the armature windings. (See Space, Clearance.)

Spark Arrester. A screen of wire netting fitting around the carbons of an arc lamp above the globe to prevent the escape of sparks from the carbons.

Spark Coil. A coil for producing a spark from a source of comparatively low electro-motive force. It consists of insulated wire wound round a core of soft iron, best a bundle of short pieces of wire. Such a coil may be eight inches long and three inches thick, and made of No. 18-20 copper wire, with a core one inch in diameter. On connecting a battery therewith and opening or closing the circuit, a spark is produced by self-induction, q. v. It is used for lighting gas.

490 STANDARD ELECTRICAL DICTIONARY.

Spark, Duration of Electric. Wheatstone determined the duration of the spark given by a Leyden jar as 1/24000 second. Feddersen by interposing a tube of water 9 millimeters (.36 inch) long in its path found that it lasted 14/10000 second, and with one 180 millimeters (7.2 inches) long, 188/10000 second. Lucas and Cazin for a 5 millimeter (.2 inch) spark, with different numbers of Leyden jars, found the following: Number of jars. Duration of Spark. 2 .000026 second 4 .000041 " 6 .000045 " 8 .000047 "

The duration increases with the striking distance, and is independent of the diameter of the balls between which it is produced.

Spark Gap. The space left between the ends of an electric resonator (see Resonator, Electric) across which the spark springs. Its size may be adjustable by a screw, something like the arrangement of screw calipers.

Sparking. In dynamo-electric machines, the production of sparks at the commutator between the brushes and commutator sections. The sparks are often true voltaic arcs, and in all cases are injurious if in any quantity, wearing out the commutator and brushes.

Sparking, Line or Points of Least. In a dynamo or electric motor the diameter of the commutator determining, or the points on the commutator marking the position of the brushes where the sparking is a minimum. Field magnets powerful in proportion to the armature are a preventative cause. The direction of the line fixes the angle of lead to be given to the brushes.

Sparking, Resistance to. The resistance to disruptive discharge through its substance offered by a dielectric or insulator. It does not depend on its insulating qualities, but on its rigidity and strength.

Spark, Length of. The length of the spark accompanying the disruptive discharge is counted as the distance from one electrode to the other in a straight line. It is longer for an increased potential difference between the two electrodes. If the gas or air between the electrodes is exhausted the length increases, until the vacuum becomes too high, when the length begins to decrease, and for a perfect vacuum no spark however small can be produced. The shape of the conductor which is discharged, the material of the electrodes, and the direction of the current are all factors affecting the length of spark producible.

491 STANDARD ELECTRICAL DICTIONARY.

Spark Tube. A tube used as a gauge or test to determine when the exhaustion of the vacuum chamber or bulb of an incandescent lamp is sufficiently high.

The interior of the tube is connected with the interior of the bulb or chamber of the lamps in process of exhaustion, and hence shares their degree of exhaustion. From time to time connections with an induction coil are made. When the exhaustion is carried far enough no discharge will take place through the vacuum. As long as the tube acts like a Geissler tube the exhaustion is not considered perfect.

Specific Heat of Electricity. The heat absorbed or given out by a fluid in passing from one temperature to another depends on its specific heat. In the Peltier and the Thomson effects. q. v., the electric current acts as the producer of a change of temperature, either an increase or decrease as the case may be. This suggests an absorption of and giving out of heat which amount of heat corresponding to a current of known amount is determinable, and may be referred to any unit of quantity such as the coulomb. This or some equivalent definite quantity of heat it has been proposed (Sir William Thomson) to term the Specific Heat of Electricity.

Spent Acid. Acid which has become exhausted. In a battery the acid becomes spent from combination with zinc. It also loses its depolarizing power, if it is a chromic acid solution or of that type, and then may be said to be spent.

Spent Liquor. The liquor of a plating bath which has become exhausted from use, the metal it contained being all or partly deposited.

Sphygmograph, Electric. An electric apparatus for recording the beat of the pulse, both as regards its rate and strength.

Sphygmophone. An apparatus for examination of the pulse by the microphone and telephone.

Spiders. Core-discs of a dynamo or motor armature are sometimes perforated with a large central aperture, are fastened together with insulated bolts, and the whole mass is secured to the shaft by three- or four-armed spiders. These are like rimless wheels, the ends of their arms being secured to the hollow cylinder constituting the armature core, and a central aperture in their hub receiving the shaft.

492 STANDARD ELECTRICAL DICTIONARY.

Spiral. This term is sometimes used instead of coil, as the primary spiral or secondary spiral of an induction coil or transformer.

Spiral Winding. The winding used on ring armatures. This may diagrammatically be represented by a spiral carried around the ring shaped core. With two field poles it gives two collecting points, positive and negative, with four field poles it gives four collecting points, alternately positive and negative.

Splice Box. A box in which the splices in underground cables and electric lines are contained. The splicing is generally done in the boxes with the cables in place. They may be two-way for straight lines, or be four-way for two side or lateral connections.

Spluttering. A term applied to a sound sometimes produced in a voltaic arc, perhaps caused by impure or insufficiently baked electrodes. (Elihu Thomson.)

Spring Control. Control of or giving the restitutive force to the needle of a galvanometer, core of a solenoid ammeter or moving part of any similar instrument by a spring. As an example see Ammeter, Ayrton's.

Fig. 307. SPRING JACKS.

Spring Jack. An arrangement for effecting, at one insertion of a species of plug, the opening or breaking of a circuit and for the simultaneous connection to the terminals formed by the breaking of two terminals of another system or loop. Thus let a line include in its circuit two springs pressing against each other, thereby completing the circuit. If a plug or wedge of insulating material were inserted between the springs so as to press them apart it would break the circuit and the whole would constitute a spring jack cut-out. If each side of the plug had a strip of brass or copper attached to it, and if the ends of another circuit were connected to these strips, then the insertion of the plug would throw the new line into the circuit of the other line.

493 STANDARD ELECTRICAL DICTIONARY.

Spring Jack Cut-out. A cut-out, of the general construction of a spring jack, q. v., except that a simple insulating plug or wedge is used in place of the metal-faced wedge with its connections of the regular spring jack. The insertion of an insulating wedge opens the circuit, which on its removal is closed. The regular spring jack wedge will operate in the same way, if its connections are kept open.

Spurious Voltage. The voltage in excess of that developed by a secondary battery which is required in the charging process. It is about .25 volt.

Square Wire. Wire whose cross-section is a square. It has been used of iron for building up the cores of armatures for dynamos or motors, for which it is peculiarly suitable, and also of copper as a winding for armatures.

Staggering. adj. When the brushes of a dynamo are set, one a little in advance of the other on the surface of the commutator, they are said to be set staggering. It is used to get over a break in the armature circuit.

State, Electrotonic. A term expressing an abandoned theory. Faraday at one time proposed the theory that a wire had to be in the electrotonic state to produce electro-motive force by movement through an electric field. Any such idea was ultimately abandoned by Faraday.

Static Breeze. The electric breeze obtained by the silent discharge of high tension electricity.

Static Electricity. Electricity at rest or not in the current form ordinarily speaking. The term is not very definite and at any rate only expresses a difference in degree, not in kind. The recognition of the difference in degree has now to a great extent also disappeared.

Station, Central. The building or place in which are placed electrical apparatus, steam engines and plant supplying a district with electric energy.

Station, Distant. The place at the further end of a telegraph line, as referred to the home station.

Station, Home. The end of a telegraph line where the operators using the expression are working.

494 STANDARD ELECTRICAL DICTIONARY.

Station, Transforming. In alternating current distribution, a building or place where a number of transformers are worked, so that low potential or secondary circuits are distributed therefrom.

Steel. A compound of iron with carbon. The carbon may range from a few hundredths of one per cent. up to two per cent. For magnets, tool steel drawn to a straw color or a little lower is good. All shaping and filing should be done before magnetization.

Steeling. The deposition of iron on copper plates by electrolysis. In electrotyping a thin deposit of iron is thus given the relief plates before printing from them. The deposit is very hard and exceedingly thin, so that it does not interfere with the perfection of the impression in the printing process. As the iron becomes worn it can be dissolved off with hydrochloric acid, which does not dissolve the copper, and a new deposit can be given it. Thus the plate may last for an indefinite number of impressions.

The iron bath may be prepared by immersing in a solution of ammonium chloride, two plates of iron, connected as anode and kathode in a circuit. One plate dissolves while hydrogen is given off from the other. The solution thus produced is used for a bath.

The hardness of the deposit, which is really pure iron, gives the name of "steeling."

Synonym--Acierage.

St. Elmo's Fire. Luminous static discharge effects sometimes seen on objects elevated in the air. They are especially noticed on ships' masts. The sailors term them corpusants (holy bodies). They resemble tongues or globes of fire.

Step-by-step Telegraphy. A system of telegraphy in which in the receiving instrument a hand is made to move step-by-step, with an escape movement around a dial. For each step there is a letter and the hand is made to stop at one or the other letter until the message is spelled out. (See Dial Telegraph.)

Step-down. adj. A qualification applied to a converter or transformer in the alternating current distribution, indicating that it lowers potential difference and increases current from the secondary.

Step-up. adj. The reverse of step-down; a qualification of a transformer or converter indicating that it raises the potential and decreases the current in the secondary.

Sticking. The adherence, after the current is cut off, of the armature to the poles of a magnet. In telegraphy it is a cause of annoyance and obstructs the working. It may, in telegraphy, be due to too weak a spring for drawing back the armature, or to imperfect breaking of the contact by the despatcher's key or by the receiver's relay.

495 STANDARD ELECTRICAL DICTIONARY.

Stopping Off. In electroplating the prevention of deposition of the plating metal on any desired portions of the object. It is effected by varnishing the places where no coating is desired. An article can be plated with silver, stopped off in any desired design, and the unvarnished portions may then be plated with gold in another bath. Various effects can be produced by such means.

Storage Capacity. A term for the ampere-hours of electricity, which can be taken in current form from a storage battery.

Storage of Electricity. Properly speaking electricity can only be stored statically or in static condensers, such as Leyden jars. The term has been popularly applied to the charging of secondary or storage batteries, in which there is really no such thing as a storage of electricity, but only a decomposition and opposite combination brought about, which leave the battery in a condition to give a current.

Storms, Electric. Wide-spread magnetic and electric disturbances, involving the disturbance of the magnetic elements and other similar phenomena. (See Magnetic Storms.)

Strain. The condition of a body when subjected to a stress. Various consequences may ensue from strain in the way of disturbance of electric and other qualities of the body strained.

Stratification Tube. A Geissler tube, q. v., for showing the stratification of the electric discharge through a high vacuum.

The stratifications are greatly intensified by the presence of a little vapor of turpentine, alcohol, bisulphide of carbon and other substances.

Stray Field. In a dynamo or motor the portion of the field whose lines of force are not cut by the armature windings.

Stray Power. The proportion of the energy wasted in driving a dynamo, lost through friction and other hurtful resistances.

Streamlets, Current. A conception bearing the same relation to an electric current that lines of force do to a field of force; elementary currents. If evenly distributed the current is of uniform density; if unevenly distributed, as in alternating currents, the current density varies in different parts of the cross section of the conductor. This evenness or unevenness may be referred to the number of streamlets per unit of area of cross-section.

[Transcriber's note: Streamlets per unit of area is redundant with current density.]

Stress. Force exercised upon a solid tending to distort it, or to produce a strain.

496 STANDARD ELECTRICAL DICTIONARY.

Stress, Dielectric. The condition of a dielectric when maintaining a charge; its two extremities are in opposite states of polarity, or are under permanent potential difference. As the two opposite polarities tend to unite a condition of stress is implied in the medium which separates them.

Stress, Electro-magnetic. The stress produced upon transparent substances in an electro-magnetic field of force. It is shown in the modified optical properties of glass and similar substances placed between the poles of a strong electro-magnet.

Stress, Electrostatic. The stress produced upon substances in an electrostatic field of force; the exact analogue of electro-magnetic stress, and affecting transparent substances in the same general way.

Striae, Electric. In Geissler tubes the light produced by the electric discharge is filled with striae, bright bands alternating with dark spaces; these may be termed electric striae.

Striking Distance. The distance that separates two conductors charged with electricity of different potential, when a spark starts between them.

Striking Solution. In silver-plating a bath composed of a weak solution of silver cyanide-with a large proportion of free potassium cyanide. It is used with a strong current and a large silver anode. This gives an instantaneous deposition of metallic silver over the surface of the article which goes to insure a perfect coating in the silver bath proper. After a few seconds in the striking solution, the article is at once removed to the plating bath.

Stripping. The removal of electroplating from an object. It may be effected in several ways. An object whose plating is to be removed is placed in a plating bath of the solution of the metal with which it is coated. It is connected as the anode to the positive plate of the battery or corresponding terminal of the generator. A kathode connected to the other terminal being placed in the bath, the coating is dissolved by electrolytic action. Sometimes simple treatment with acid is employed. Different stripping baths are described under the heads of the different metals.

S. U. Symbol or abbreviation for Siemens' Unit of Resistance. (See Resistance, Siemens' Unit of.)

Sub-branch. A branch or lead of wire taken from a branch lead: a term used in electric distribution.

Sub-main. In electric distribution a conductor connected directly to a main; a branch.

497 STANDARD ELECTRICAL DICTIONARY.

Subway, Electric. A subterranean system of conduits for electric cables. As generally constructed in this country it includes manholes, q. v., at the street corners connected by ducts or pipes. These pipes are large enough to hold a cable. To introduce a cable into a duct, which latter may be two or three inches in diameter, and from two hundred to six or seven hundred feet long, a wire or rope is first passed through the duct. This is done by a set of short wooden rods with screws at the end so as to be screwed together. Each rod must be shorter than the diameter of the manhole. A rod is thrust in, another is screwed to it and thrust in, and thus a set of rods is made to extend as far as desired. In pulling them out a rope is attached and drawn through. This rope or a larger one is used in drawing the cable through the duct. A windlass is employed to draw the rope with cable attached through the ducts.

Sulphating. In storage battery cells, the formation of a hard white basic lead sulphate, Pb2 S05. Its formation is due to over-exhaustion of the cells. As long as the voltage is not allowed to fall below 1.90 volts per cell little of it forms. As it accumulates it is apt to drop off the plate and fall to the bottom, thus weakening the plate possibly, and depriving it of active material, and clogging up the cell. If it carries a film of metallic lead with it, there is danger of short circuiting the cell.

The presence of some sodium sulphate in the solution is said to tend to prevent sulphating, or to diminish it.

Sulphur Dioxide.
A compound gas, S O2; composed of
Sulphur, 32
Oxygen, 32
Molecular weight, 64
Specific gravity, 2.21.

It is a dielectric of about the same resistance as air. Its specific inductive capacity at atmospheric pressure is: 1.0037 (Ayrton).

Synonyms--Sulphurous Acid--Sulphurous Acid Gas.

Sunstroke, Electric. Exposure to the arc light sometimes produces the effects observed in cases of sunstroke. It is said that, in the case of workmen at electric furnaces, these effects are very noticeable. (See Prostration, Electric.)

[Transcriber's note: Effects are due to ultraviolet light.]

Supersaturated. adj. A liquid is supersaturated when it has dissolved a substance at a temperature favorable to its solubility and its temperature has been allowed to change, the liquid being kept free from agitation or access of air, provided crystallization or precipitation has not taken place. It expresses the state of a liquid when it holds in solution more than the normal quantity of any substance soluble in it.

Surface. A galvanic battery is arranged in surface when all the positive plates are connected together and all the negative plates are also connected. This makes it equivalent to one large cell, the surface of whose plates would be equal to the aggregate surface of the plates of the battery. It is also used as an adjective, as "a surface arrangement of battery."

498 STANDARD ELECTRICAL DICTIONARY.

Surface Density. The relative quantity of an electric charge upon a surface.

Surface, Equipotential. A surface over all of which the potential is the same. In a general sense equipotential surfaces are given by planes or surfaces which cut lines of force at right angles thereto, or which are normal to lines of force. The conception applies to electrostatic and electro-magnetic fields of force, and for current conductors the planes normal to the direction of the current are equipotential surfaces.

The contour of an equipotential surface of a field of force which is drawn or represented by delineations of its lines of force can be obtained by drawing a line normal thereto. This line will ordinarily be more or less curved, and will be a locus of identical potentials.

An electric equipotential surface may be described as electro-static, electro- magnetic, or magnetic; or may be an equipotential surface of a current conductor. Besides these there are mechanical and physical equipotential surfaces, such as those of gravitation.

Surface Leakage. Leakage of current from one part of an insulating material to another by the film of moisture or dirt on the surface.

Suspension. This term is applied to methods of supporting galvanometer needles, balance beams, magnetic compass needles and similar objects which must be free to rotate. (See Suspension, Bifilar--Fibre and Spring Suspension--Fibre Suspension--Knife Edge Suspension--Pivot Suspension--Suspension, Torsion.)

308. DIAGRAM OF BIFILAR SUSPENSION.

Suspension, Bifilar. Suspension by two vertical parallel fibres, as of a galvanometer needle. The restitution force is gravity, the torsion being comparatively slight and negligible. Leaving torsion out of account the restitution force is (a) proportional to the distance between the threads;. (b) inversely proportional to their length; (c) proportional to weight of the needle or other object suspended; (d) proportional to the angle of displacement.

499 STANDARD ELECTRICAL DICTIONARY.

Assume two masses A and B at the end of a weightless rod, suspended by the parallel cords a A, b B. Let the rod be rotated through an angle theta. Consider the cord a A. Its lower end is swung through the angle theta, as referred to the center O; the cord is deflected from the vertical by an angle psi, such that a A tang(psi)= O A 2 sin (theta/2). The component of gravitation tending to restore A to A, acting towards A is equal to m g tan(psi). Its moment around O is equal to (m g tan(psi)) * (O A cos(theta/2). The whole moment of the couple is 2 m g tan(psi). 0 A. cos(theta/2) = 2 m g (O A2/ a A) 2 sin(theta/2). Cos(theta/2) = 2mgl(OA2/aA) sin(theta). The moment of the restoring force is thus proportional to the sine of the angle of deflection, and the oscillations of such a system are approximately simple harmonic. (Daniell.)

If the twisting is carried so far as to cause the threads to cross and come in contact with each other the suspension ceases to be a bifilar suspension, but assumes the nature of a torsional suspension.

[Transcriber's note: This is the image of the first paragraph.]

Swaging, Electric. Mechanical swaging in which the objects to be swaged are heated by an electric current as in electric welding.

S. W. G. Abbreviation for Standard Wire Gauge.

Fig. 309. SIMPLE SWITCH.

Switch. A device for opening and closing an electric circuit.

A simple type is the ordinary telegrapher's switch. A bar of metal is mounted horizontally by a pivot at one end, so as to be free to rotate through an arc of a circle. In one position its free end rests upon a stud of metal. One terminal of a circuit is attached to its journal, the other to the stud. Resting on the stud it closes the circuit, in other positions it opens the circuit.

500 STANDARD ELECTRICAL DICTIONARY.

Switch, Automatic. A switch opened and closed by the electric current. It is used for lighting distant incandescent lamps. It includes one or two electro-magnets operated by two push buttons. In the usual arrangement one button is black and the other white, for extinguishing and lighting respectively. When the white button is pushed it causes a current to pass through one of the electro-magnets. This attracts its armature, thereby making a contact and throwing the lamps into the lighting circuit. Then they remain lighted until the black button is pressed. This excites the other magnet, which attracts its armature, breaks the contact and extinguishes the lights.

The object of the automatic switch is to enable distant lamps to be lighted without the necessity of carrying the electric leads or wires to the place whence the lighting is to be done. A very small wire will carry enough current to operate the magnets, and open circuit batteries, such as Leclanché batteries, may be used as the source of current for the switch, but generally the lighting current is used for the purpose.

A single magnet may do the work. When the lighting button is pressed the magnet is excited, attracts its armature and holds it attracted, until by pressing the black button the current is turned off from it. In this case the lighting current is used to excite the magnet.

Switch Board. A board or tablet to which wires are led connecting with cross bars or other switching devices, so as to enable connections among themselves or with other circuits to be made.

Switch, Circuit Changing. A switch whose arm in its swing breaks one contact and swinging over makes another. It is employed to change the connections of circuits from one dynamo to another.

Synonyms--Changing Switch--Changing Over Switch.

Switch, Double Break. A form of switch in which double contact pieces are provided to give a better contact. One form consists of a hinged bar whose end swings down between two pairs of springs. Both pairs are connected to one terminal, and the bar to the other terminal of a circuit.

Switch, Double Pole. A heavy switch for central station work, that connects and disconnects two leads simultaneously.

Switch, Feeder. A heavy switch, often of double contact type, for connecting and disconnecting feeders from bus bars in central stations.

501 STANDARD ELECTRICAL DICTIONARY.

Switch, Knife. A switch whose movable arm is a narrow, deep bar of copper or brass, and which in making contact is forced in edgeways between two springs connected to one terminal. The bar is connected to the other terminal.

Synonyms--Knife Break Switch--Knife Edge Switch.

Switch, Multiple. A switch which in the swing of its bar connects one by one with a number of contacts so that ultimately the end of its bar is in contact with all at once. It is used to throw lights in and out in succession, and it can, if the multiple contacts connect with resistances, make them operate as a rheostat.

Switch, Pole Changing. A switch for changing the direction of the current in a circuit.

Switch, Reversing. A switch, often of the plug type (see Plug Switch) for changing the direction of current passing through a galvanometer.

Switch, Snap. A switch constructed to give a quick, sharp break. It has a spiral spring interposed between the handle and arm. As the handle is drawn back to open it the spring is first extended, the bar being held by the friction of the contacts, until the spring suddenly jerks it up, thus breaking the contact.

Switch, Storage Battery Changing. A switch for changing storage battery connections from series to multiple and back again.

Switch, Three Way. A switch, so constructed that by turning its handle connection can be made from one lead to either of two other leads, and also so that connection can be completely cut off.

Sympathetic Vibration. The establishment of periodic movement in one body by impulses of the same period communicated to it from another body in motion. Thus if two tuning forks are of the same pitch and one is sounded the other will begin to sound by sympathy, the sound waves communicating the necessary periodic impulses to it.

Sympathetic vibrations are utilized in harmonic telegraphy. (See Harmonic Receiver--Telegraph, Harmonic.)

T. Symbol of time.

Tailings. (a) In high speed transmission of telegraph signals by the automatic system, the definiteness of the signal marks is sometimes interfered with by retardation. Wrong marks are thus produced called tailings.

(b) The prolongation of the current at the distant receiving station of a telegraph line due to the discharge of the line and to self-induction.

Synonyms--Tailing--Tailing Current.

502 STANDARD ELECTRICAL DICTIONARY.

Tamidine. Reduced nitro-cellulose. Nitro-cellulose is dissolved in a proper solvent and is obtained by evaporation as a translucent solid mass. By ammonium sulphide or other reagent it is reduced so as to be virtually cellulose. It is cut into shape for filaments of incandescent lamps, which shapes are carbonized and flashed.

Tangent Law. In a galvanometer the tangents of the angles of deflection of the needle are proportional to the deflecting force--

I. When the controlling force is unaltered in absolute magnitude and direction by the motion of the needle.

II. When the deflecting force acts at right angles always to the controlling force.

These conditions are usually secured by having the actuating coil through which the current passes flat and of large diameter compared to the length of the needle; by using the uniform field of the earth as the control; by having a short needle; by placing the coil with its plane in the magnetic meridian.

For best proportions of tangent galvanometer coils see Bobbins.

Fig. 310. GRAPHIC CONSTRUCTION OF TANGENT SCALE.

Tangent Scale. An arc of a circle in which the number of graduations in any arc starting from zero are proportional to the tangent of the angle subtended by such arc. The system is for use with tangent galvanometers. Thus if for 45° a value of 100 is taken and marked on the scale then for the arc 26° 33' + a value of 50 should be marked on the scale because such are the relative values of the tangents.

Thus the scale instead of being divided into degrees is divided into arcs of varying length, growing shorter as they are more distant from the zero point, of such length that the first division being subtended by a tangent of length 1, the first and second divisions added or taken together as one arc are subtended by a tangent of length 2, and so on.

In the cut a simple method of graphically laying out a tangent scale is shown. In it C is the centre of the arc, and H the radius running to the zero of the instrument. From C a circle is described and on H a vertical line tangent to the arc is erected. Taking any part of the tangent, as the length shown ending at D, it is divided into any number of equal parts. Radii of the circle are now drawn whose prolongations pass through the divisions on the tangent. These radii, where they intersect the arc of the circle, determine equal divisions of the tangent scale, which, as is evident from the construction, are unequal angular divisions of the arc.

503 STANDARD ELECTRICAL DICTIONARY.