(b) 1 foot long 1/1000 inch thick, 58.45 "
(c) 1 meter long weighing 1 gram, .7570 "
(d) 1 meter long, 1 millimeter thick, .1237 "
Percentage increase in resistance per degree C. (1.8? F.) at about 20? C. (68?F.), about 0.5 per cent.
Resistance of a 1 inch cube, 3.825 microhms.
Electro-chemical equivalent (Hydrogen = .0105), .147 and .294
Iron, Electrolytic.
Iron deposited by electrolytic action. Various baths are employed for its formation. (See Steeling.) It has very low coercive power, only seven to ten times that of nickel.
Ironwork Fault of a Dynamo.
A short circuiting of a dynamo by, or any connection of its coils with, the iron magnet cores or other iron parts.
Isochronism.
Equality of periodic time; as of the times of successive beats of a tuning fork, or of the times of oscillations of a pendulum.
Isoclinic Lines.
The lines denoting the locus of sets of equal dips or inclinations of the magnetic needle upon the earth"s surface, the magnetic parallels, q.
v. These lines are very irregular. (See Magnetic Elements.)
Isoclinic Map.
A map showing the position of isoclinic lines.
Isodynamic Lines.
Lines marking the locus of places of equal magnetic intensity on the earth"s surface. (See Magnetic Elements, Poles of Intensity.)
Isodynamic Map.
A map showing the position of isodynamic lines. (See Poles of Intensity.)
Isogonic Lines.
Lines on a map marking the locus of or connecting those points where the declination or variation of the magnetic needle is the same. (See Magnetic Elements--Declination of Magnetic Needle.)
Synonyms--Isogonal Lines--Halleyan Lines.
309 STANDARD ELECTRICAL DICTIONARY.
Isogonic Map.
A map showing the isogonic lines. On such a map each line is characterized and marked with the degrees and direction of variation of the compa.s.s upon itself.
Synonym--Declination Map.
Isolated Plant, Distribution or Supply.
The system of supplying electric energy by independent generating systems, dynamo or battery, for each house, factory or other place, as contra-distinguished from Central Station Distribution or Supply.
Isotropic.
(Greek, equal in manner.)
Having equal properties in all directions; the reverse of anisotropic, q. v. Thus a h.o.m.ogeneous ma.s.s of copper or silver has the same specific resistance in all directions and is an isotropic conductor. Gla.s.s has the same specific inductive capacity in all directions and is an isotropic medium or dielectric. The same applies to magnetism. Iron is an isotropic paramagnetic substance. (See Anisotropic.) The term applies to other branches of physics also.
I. W. G.
Contraction for Indian Wire Gauge--the gauge adopted in British India.
J.
Symbol for the unit joule, the unit of electric energy.
Jacobi"s Law.
A law of electric motors. It states that the maximum work of a motor is performed when the counter-electromotive force is equal to one-half the electro-motive force expended on the motor.
Jewelry.
Small incandescent lamps are sometimes mounted as articles of jewelry in scarf-pins or in the hair. They may be supplied with current from storage or from portable batteries carried on the person.
Joint, American Twist.
A joint for connecting telegraph wires, especially aerial lines. Its construction is shown in the cut. The end of each wire is closely wound around the straight portion of the other wire for a few turns.
Fig. 203. AMERICAN TWIST JOINT.
310 STANDARD ELECTRICAL DICTIONARY.
Joint, Britannia.
A joint for uniting the ends of telegraph and electric wires. The ends of the wires are sc.r.a.ped clean and laid alongside each other for two inches, the extreme ends being bent up at about right angles to the wire. A thin wire is wound four or five times around one of the wires, back of the joint, the winding is then continued over the lapped portion, and a few more turns are taken around the other single wire.
The whole is then soldered.
Fig. 204. BRITANNIA JOINT.
Joint, b.u.t.t.
A joint in belting or in wire in which the ends to be joined are cut off square across, placed in contact and secured. It ensures even running when used in belting. Any irregularity in thickness of a belt affects the speed of the driven pulley. As dynamos are generally driven by belts, and it is important to drive them at an even speed to prevent variations in the electro-motive force, b.u.t.t joints should be used on belting for them, unless a very perfect lap joint is made, which does not affect either the thickness or the stiffness of the belt.
When a b.u.t.t joint is used in wire a sleeve may be used to receive the ab.u.t.ting ends, which may be secured therein by soldering. This species of joint has been used on lightning rods and may more properly be termed a sleeve joint.