Leyden Jar

a well known piece of electrical apparatus. It was invented in 1746 by Cuneus, a professor in the University of Leyden, Holland. The jar is simply a condenser. It consists essentially of a jar coated within and without with tin foil for about two-thirds of the height. A brass rod passes inside, through a stopper, a chain connects the inner end of the rod with the inner coating. The outer end of the rod terminates in a knob. The jar may be charged by bringing one of the coatings into connection with the conductor of an electrical machine and connecting the other coating with the ground. The coats will become charged with opposite kinds of electricity which attract each other but are kept apart by the glass wall of the jar. If the knob be connected with the outer coating the charges leap together. If the outer coating be touched with one hand and the knob with the other, the charge will pass through the body, imparting a shock, which, in the case of a large jar powerfully charged, is sufficient to cause death. The ordinary strokes of lightning are discharges of a similar nature. The earth and a cloud are the coatings; the air which separates takes the place of the glass of the jar. The bolt of lightning is the discharge.