If the body is perfectly electrified, as when the glass tube
is used^ and a pointed wire er needle be presented to it,

a bright spark will be
A s seen upon its point, as

represented at B, in
the figure. If the body
is negatively electri-
fied, and a pointed
wire be presented to
it, a luminous brush
will appear on it^
point, as shown on A.
In the first case we may suppose the positive fluid to be
passing on at the point, or the negative fluid to be passing
off, for the effect is the same ; so, in the second case,
when the brush of light appears, we may consider the
positive fluid as passing off from the point, or the nega-
tive fluid as passing on, the result being the same.
Effect of Points. — Electricity can not be long pre-
served on a body, even when well insulated, if there are
any points projecting from it, as the fluid passes freely
and silently from points into the air, and is lost. Nor
can the fluid be retained on an insujated body if there
are points of other inducting bodies near turned toward
it. The fluid will escape rapidly to these points, and be
conveyed away.
549. Both Electricities always excited simultaneously.
