The Wimshurst Machine was developed between 1880 and 1883 by James Wimshurts. It is an electrostatic device created for the purpose of generating high voltages. It has two contra-rotating discs on a vertical spine with two cross bars, metallic brushes, and a spark gap. It is an influence machine because it creates electric charges through electrostatic induction. It is self-starting but does need mechanical power initially to rotate the disks. The current produced is constant and proportional to the size of the metals disks and the rate at which they are rotating. The Leyden Jar is an early storage device for electric charge. It was the first capacitor. The original form of the device was just a glass bottle partially filled with water, with a metal wire passing through a cork closing it. Soon it was found that it was better to coat the exterior of the jar with metal foil, leaving the impure water inside acting as a conductor. Franklin invented his electric bells in the middle of the 18th century when noticed that a pith ball or cork would initially be attracted to a charged object, but if the two touched the ball would be repelled. He realized that this was because the two objects were initially charged differently but once they touched they took on the same charge. Franklin realized that if he replaced the charged object with a bell, he could make an "electric bell." He soon found practical use for his bell as a lightning detector. When connected it to his lightning rod, the bell would ring whenever an electrical storm was nearby.