large hollow cylinders of brass with globular ends, each supported by
two glass pillars, constitute the reservoir for receiving the
electricity. They are called the _prime conductors_, and are supplied
with U-shaped rods of metal, furnished with points along their sides,
called _combs_, for the purpose of receiving the electricity from the
glass plate, the arms of the U being held upon either side. The other
ends of the conductors are connected by a rod from the middle of which
projects another rod terminating in a knob, for delivering the spark.

On turning the plate, a faint snapping sound is heard, and when the
room is darkened, a spark is seen to be thrown out from the knob
projecting from the _prime conductors_.

Many curious and interesting experiments may be performed by means of
the machine, illustrating the general properties of electricity. For
instance: a person standing on an insulated bench, that is, a bench
with glass legs, or having the legs resting on glass, and having one
hand on the conductor, can send sparks, with the other hand, to
everything and everybody about. This illustrates communication of
electricity by contact. A wooden head, covered with long hairs, when
placed on the conductor, illustrates electrical repulsion, by the
hairs standing on end.

If the hand is held to the knob, sparks will pass from it in rapid
succession, causing in the hand a sensation of pain. This is called an
_electric shock_, and is caused by the electric fluid occasioning a
sudden motion by the contraction of the muscles through which it
passes. The force of the shock is in proportion to the power of the
machine.