Gravity, Acceleration of.
The velocity imparted to a body in one second by the action of
gravitation at any standard point upon the earth's surface in a vacuum.
This will vary at different places, owing principally to the variation
in centrifugal force due to the earth's rotation. For standard valuation
it must be reduced to sea level. The following are examples of its
variation:
Equator, 978.1028 centimeters per second
Paris, 980.94 "
Greenwich 981.I7 "
Edinburgh, 981.54 "
Pole (N. or S.), 983.1084 (theoretical) "
As round numbers for approximate calculations 981 centimeters or 32.2
feet may be employed.
[Transcriber's note: The acceleration of gravity at the equator is also
reduced by the increased distance from the center of the earth
(equatorial bulge). Increased altitude reduces gravity. Reduced air
density at altitude reduces buoyancy and increases apparent weight.
Local variations of rock density affects gravity.]
Gravity, Control.
Control by weight. In some ammeters and voltmeters gravity is the
controlling force.
Grid.
A lead plate perforated or ridged for use in a storage battery as the
supporter of the active materials and in part as contributing thereto
from its own substance.
Ground.
The contact of a conductor of an electric circuit with the earth,
permitting the escape of current if another ground exists.
Ground-wire.
A metaphorical term applied to the earth when used as a return circuit.
Fig. 192. GROVE'S GAS BATTERY.
Grove's Gas Battery.
A voltaic battery depending for its action on the oxidation of hydrogen
instead of the oxidation of zinc. Its action is more particularly
described under Battery, Gas. In the cut B, B1 * * * are the terminals
of the positive or hydrogen electrodes, marked H, and A, Al * * * are
the terminals of the negative or oxygen electrodes marked O, while M, M1
* * * is dilute sulphuric acid.