Alternative Path.
A second path for a current appearing as a disruptive
discharge. Where two paths are offered the discharge, as it is of
alternating or oscillatory type, selects the path of least
self-induction. Thus a thick bar of copper, with no air gap, may be
abandoned by the current in favor of a small iron wire with an air gap,
but which has less self-induction.
The lightning arresters, q. v., for the protection of telegraph offices
are sometimes based on these principles. A path of very high resistance
but of small self-induction is offered between the line and the earth.
This the lightning discharge selects in preference to the instruments
with their iron cores, as the latter are of very high self-induction.
Alternator.
A dynamo electric generator supplying an alternating current. (See
Dynamo, Alternating Current.)
Synonym--Alternating current generator or dynamo.
Alternator, Constant Current.
An alternating current dynamo supplying a current of unvarying virtual
amperage. Alternators of this type are constructed with an armature of
high self-induction. Sometimes fine winding contained in deep peripheral
notches in the core-discs is employed to magnify the self-induction.
Such generators are employed for series lighting, especially
arc-lighting.
Aluminum.
A metal; one of the elements; symbol: Al.
Atomic weight: 27.4. Equivalent: 9.13. Valency: 3.
Specific gravity: 2.6. It is a conductor of electricity.
Relative resistance annealed, (Silver = 1) 1.935
Specific resistance at 0ºC (32°F.) 2.912 microhms
Resistance of a wire at 0ºC (32°F.)
a) 1 foot long, weighing 1 grain, 0.1074 ohms.
b) 1 foot long, 1/1000 inch thick, 17.53 "
c) 1 meter long, weighing 1 gram, 0.0749 "
d) 1 meter long, 1 millimeter thick 0.03710 "
Resistance of a 1-inch cube at 0ºC (32°F.) 1.147 microhms
Electro-chemical equivalent. .0958 (hydrogen == .0105)