Leyden jar

A gla j. coated on the inside and outside with tinfoil, the inner coating having in contact with it a metallic rod which projects from the mouth of the j. and terminates in a knob. The j. is charged by placing the knob in contact with a static machine and putting the outside coating in communication with the ground by a metallic knob brought near the j. Sparks are thus drawn from the machine to the inner coating and are lodged upon the surface of the gla . The j. is discharged by placing one knob of the discharging rod in contact with the outer coat and turning the other knob close to the inner coating, from which a spark is immediately elicited. [Described by van Mu chenbroek in Leyden, Holland, in 1746.]