ELECTRICAL MACHINE, a machine nor converting mechanical work, either by friction or by induction, into electric energy. The earliest known form was constructed about the middle of the 17th century by Otto von Guericke. It con sisted of a ball of sulphur mounted on an axle which was rotated as rapidly as possible while the hand of the operator was pressed against the ball. The fric tion of the hand upon the sulphur gen erated electricity. Sir Isaac Newton replaced the sulphur ball with a glass globe, and later workers substituted woolen cloth or pieces of leather for the hand. In 1768, Jesse Ramsden con structed the first plate electrical ma chine, consisting of a glass disc, which was rotated rapidly between two leather rubbers. The glass became positively is brought near to an electrified sub stance having a positive charge. Then negative electricity is attracted by the charged body, while positive electricity is repelled, and if the conductor be con nected with the earth, the positive elec tricity will escape, leaving the conductor charged with negative electricity. This is the underlying principle of the in fluence machine. In the Topler machine, for instance, two glass discs are used, one of which is fixed, while the other will revolve. On the latter are fixed a num
ber of strips of tinfoil and, on the other, two so-called "field-plates," also made of tin-foil. A charge is given to one of the field plates, and then the movable plate is revolved. Let us suppose that the charge on the field plate is positive. Then as a tin-foil strip moves into place op posite the field plate, negative electricity is attracted and positive electricity re pelled. A brass wire brush makes con tact with the metallic strip and the positive electricity escapes, leaving the strip charged with negative electricity. Another strip moves into place, and the same process is repeated. In the mean time, the first strip has moved on toward metal collecting combs, and communi cates its charge to them. The electricity from combs passes to Leyden jars, where it is stored.
The more modern Wimshurst machine resembles the Topler, but consists of two glass plates, each fitted with tin-foil discs, and each made to revolve in the opposite direction to the other.