ELECTRIC MACHINE

used largely as a therapeutic agent in exciting an electric current, either by friction or by static induction. The first type is based on the principle that gla or sealing wax, when subjected to friction, produces an electric flow. There are many varieties of this type, but in its simplest form it consists of a gla cylinder being turned rapidly, usually by hand. What fs called a ‘rubber,’ a cushion of leather filied with horsehair, attached to a movable frame, is pre ed up against the ' revolving gla , a silk flap attached to the ‘rubber’ being thrown half over the cylinder. The flow of electricity generated pa es through the metal frame to which the cushion is attached. The second type of electric machine is based on the old electrophorus. A cake of amber or vulcanite, from 12 to 15 inches in diameter and about an inch thick, rests on an iron plate. A metal disc, with an insulated handle, somewhat smaller in diameter than the vulcanite plate, is laid on top of the Yatter after it has been rubbed th dry flannel. Since the vulcanite is a non-conductor, the negative electricity enerated by the rubbing pa es out of t py at the points of contact with the metal disc, which is at not more than three or four points. Enough current may thus be generated to charge a Leyden jar.