Pistol, Electric.
An experimental apparatus for exhibiting the power of electric
incandescence or of the electric spark. A tube is mounted with a handle
like a pistol. A plug is provided to screw in and out of its side. The
plug carries two wires connected on its inner side by a fine platinum
wire, or else disconnected but with their ends brought near together to
act as terminals for the production of a spark. To use it the tube is
filled with a mixture of air and gas, the latter either hydrogen,
hydro-carbon or other combustible gas. The tube when full is corked. The
wire is heated to incandescence by a current, or a spark is passed from
a Leyden jar or other source of electrostatic excitation. The mixture,
if properly proportioned, explodes and expels the cork violently.
Fig. 264. ELECTRIC PISTOL.
Pith.
A light and soft cellular tissue forming the central core of exogenous
trees and plants. In the older parts of the tree the woody tissue often
encroaches in and partly obliterates it.
For electrical pith-balls, the pith of the elder, of corn, or, best of
all, of sun-flower stems is used.
Pith-balls.
Ball made of pith. They are used in the construction of electroscopes
and for other experiments in static electricity.
They are cut out with a sharp knife and their shape may be improved by
gentle rolling in the hand or between the fingers.
Pivot Suspension.
Suspension poising or supporting of an object on a sharp pivot. This is
used for the needle in the ordinary compass. A cavity or inverted cup,
which may be made of agate, is attached to the middle of the needle
which has a hole for its reception. The centre of gravity of the needle
comes below the bottom of the cup.
Pivot suspension is not perfect, as it has considerable friction. There
is no restitution force, as with torsion filaments.