Law of Successive Temperatures.
A law of thermo-electricity. The electro-motive force due to a given
difference of temperature between the opposite junctions of the metals
is equal to the sum of the electro-motive forces produced by fractional
differences of temperature, whose sum is equal to the given difference
and whose sum exactly fills the given range of temperature.
Law, Right-handed Screw.
This rather crude name is given by Emtage to a law expressing the
relation of direction of current in a circuit to the positive direction
of the axis of a magnet acted on by such current. It is thus expressed:
A right-handed screw placed along the axis of the magnet and turned in
the direction of the current will move in the positive direction, i. e.,
towards the north pole of the axis of the magnet.
Lead.
A metal; one of the elements; symbol Pb. Atomic weight, 207;
equivalent, 103-1/2; valency, 2.
Lead may also be a tetrad, when its equivalent is 51.75.
The following data are at 0º C. (32º F.) with compressed metal:
Relative Resistance, (Silver = l) 13.05
Specific Resistance, 19.63 microhms.
Resistance of a wire,
(a) 1 ft. long, weighing 1 grain, 3.200 ohms.
(b) 1 meter long, weighing 1 gram, 2.232 "
(c) 1 meter long, 1 millimeter thick, .2498 "
Resistance of 1 inch cube, 7.728 microhms.
Electro-Chemical Equivalent (Hydrogen = .0105) 1.086 mgs.
Leading Horns.
The tips of pole pieces in a dynamo, which extend in the direction of
movement of the armature.
Leading-in Wires.
The platinum wires passing through the glass of an incandescent
lamp-chamber, to effect the connection of the carbon filament with the
wires of the circuit.
Lead of Brushes, Negative.
In a motor the brushes are set backwards from their normal position, or
in a position towards the direction of armature rotation or given a
negative lead instead of a positive one, such as is given to dynamo
brushes.
Leak.
A loss or escape of electricity by accidental connection either with the
ground or with some conductor. There are various kinds of leak to which
descriptive terms are applied.
Leakage.
The loss of current from conductors; due to grounding at least at two
places, or to very slight grounding at a great many places, or all along
a line owing to poor insulation. In aerial or pole telegraph lines in
wet weather there is often a very large leakage down the wet poles from
the wire. (See Surface Leakage--Magnetic Leakage.)