It is a conductor of electricity.

Relative resistance, compressed, (Silver = 1) 8.784 Specific resistance at 0? C. (32? F.), 13.21 microhms.

Resistance of a wire at 0? C. (32? F.), (a) 1 foot long, weighing 1 grain, 1.380 ohms.

(b) 1 foot long, 1/1000 inch thick, 79.47 "

(c) 1 meter long, weighing 1 gram, .9632 "

(d) 1 meter long, 1 millimeter thick, .1682 "

Resistance of a 1 inch cube at 0? C. (32? F.), 5.202 microhms.

Percentage of variation in resistance per degree C. (1.8? F.), at about 20? C. (68? F.), .0365 Electro-chemical equivalent (hydrogen = .0105), .619 mgs.

.310 "

542 STANDARD ELECTRICAL DICTIONARY.

Tinnitus, Telephone.

A nervous affection of the ear, of the order of professional cramp; it is attributed to too much use of the telephone.

Tin Sounders.

A recent addition to the single needle telegraph. (See Telegraph, Single Needle.) It consists of small tin plates, cut and bent, and so fitted in pairs to the instrument, that the needle as deflected strikes one or the other on its right and left hand movements. The sounders can be made to give sufficiently distinctive sounds to make sound-reading, q. v., possible. Commercial tin plate, which is really tinned iron, seems to give the best results.

Fig. 337. TIN SOUNDERS.

Tissandier's Solution.

A solution for bichromate batteries. It is composed as follows: Water, 100 parts by weight pota.s.sium bichromate, 16 parts 66? sulphuric acid, 37 parts.

Tongue of Polarized Relay.

The German silver extension of the vibrating or oscillating member of a polarized relay, corresponding to the armature of an ordinary relay.

Tongue of Polarized Relay, Bias of.

In a Siemens' polarized relay the pole pieces are adjustable so that they may be brought nearer to or withdrawn from the tongue. One of the poles is adjusted so as to be nearer the tongue. This one-sided adjustment is the bias. Its effect is that when the relay is unexcited this pole attracts the armature so that it normally is drawn towards it.

This ensures the normal contact of the tongue either with the contact point, or with the insulated stop piece or adjustment screw. Without bias the armature remains in contact with or drawn towards whichever pole it was last attracted to. In its usual use a bias is given it.

Top, Magnetic.

A toy ill.u.s.trating magnetic attraction. It consists of a disc or body of lead or other material, through which a magnetized steel spindle pointed at its lower end is thrust. A number of short pieces of iron wire are used with it. It is spun like an ordinary top upon the point of the spindle and one of the pieces of iron wire is laid by the side of its point. As it turns the magnetic adherence causes the piece of wire to be carried along in one direction by the rotation of the spindle, until the end is reached, when it goes over to the other side of the spindle and travels back again.

By using bent pieces of wire of various shapes the most curious effects are produced. Circles and S shaped pieces give good effects. To increase the mysterious effect covered iron wire (bonnet wire) may be employed.

Fig. 338. MAGNETIC TOP.

543 STANDARD ELECTRICAL DICTIONARY.

Torpedo, Electric.

(a) A fish, the Raia Torpedo, which possesses the power of giving electric shocks. (See Ray, Electric.)

(b) An instrument of war; a torpedo whose operations include electrical discharge or other electric function or factor of operation.

Torpedo, Sims-Edison.

A torpedo driven by an electric motor, and also steered by electricity.

Its motions are all controlled from the sh.o.r.e. The torpedo proper is carried some distance below the surface of the water by a vessel immediately above it, from which it is suspended by two rigid bars. In the torpedo is a cable reel on which the conducting cable is disposed.

An electric motor and controlling gear are also contained within the torpedo. In its front the explosive is placed. It is driven by a screw propeller actuated by the electric motor. As it moves it pays out cable so that it has no cable to draw after it through the water, the cable lying stationary in the water behind it. This avoids frictional resistance to its motion. The maintenance of the torpedo at a proper depth is one of the advantages of the system.

544 STANDARD ELECTRICAL DICTIONARY.

Torque.

A force tending to produce torsion around an axis. An example is the pulling or turning moment of an armature of an electric motor upon its shaft. It is often expressed as pounds of pull excited at the end of a lever arm one foot long.

The expression is due to Prof. James Thompson, then of the University of Glasgow.

"Just as the Newtonian definition of force is that which produces or tends to produce motion (along a line), so torque may be defined as that which produces or tends to produce torsion (around an axis). It is better to use a term which treats this action as a single definite ent.i.ty than to use terms like 'couple' and 'moment,' which suggest more complex ideas." (S. P. Thompson.)

A force, acting with radius r gives a torque equal to f X r ; f and r may be expressed in any units. S. P. Thompson gives the following equivalents :

To reduce dyne-centimeters to gram centimeters, divide by 981 dyne-centimeters to meter-kilograms divide by 981E5 dyne-centimeter, to pound-feet divide by 13.56E6 pound-feet to meter-kilograms divide by 7.23

In each of these compound units the first unit is the force and the second unit is the radius or lever arm of the torque.

Synonyms--Turning Moment--Moment of Couple--Axial Couple--Angular Force--Axial Force.

Torsion Balance, Coulomb's.

Originally an apparatus in which electrostatic attraction or repulsion is measured against the torsion of a filament, often of silk-worm coc.o.o.n fibre. It consists in one form of a cylindrical gla.s.s vessel in which a light sh.e.l.lac needle is suspended horizontally by a fibre. This needle carries at one end a gilded disc or sphere and is suspended by a fine wire, or filament. A proof plane, q. v., is excited by touching it to the body under trial; it is then inserted in the case. The disc on the needle is first attracted and then repelled. The position finally taken by the needle is noted. The force of torsion thus produced is determined by twisting the filament by the torsion head on the top of the apparatus so as to move the needle a certain distance towards the proof plane. The more the torsion-head has to be turned to carry the needle through a specified arc the greater is the torsion effected or the greater is the repulsion exerted, The torsional force of a wire is proportional to the angle of torsion; this gives the basis for the measurement.

With magnetic needle it is used to measure magnetic repulsion and attraction. The best material for the filament is quartz, but the instrument is not very much used.

Torsion Galvanometer.

A galvanometer in which the torsion required to bring the index back to zero, when the current tends to displace it, is made the measure of the current strength or of the electro-motive force. It involves the use of a torsion head, q. v., or its equivalent.

545 STANDARD ELECTRICAL DICTIONARY.

Torsion Head.

The handle and disc from whose undersurface the filament depends to which the needle or magnet is attached. It is turned to measure the torsional effect, the edge of the disc being marked or graduated so as to give the angle of deflection required to overcome the effect of the torque of the needle.

Torsion Suspension.

Suspension by one or more wires, fibres, or ribands, involving the rest.i.tutive force of torsion. Thus fibre suspension, q. v., is a variety of torsion suspension.