Electrical equipment. Historical artwork of electrical equipment used by Benjamin Franklin (1706-90), American scientist and statesman. At top, upper left and lower right are some Leyden jars, the earliest form of capacitor, a device for storing electricity. At upper centre is a sentry box with a metal rod through it. This was to be attached to a church spire to test whether lightning was made of electricity and so could be conducted. However, a kite (upper centre) was used successfully instead. He proved that there was positive and negative charge. These diagrams are from Experiments and Observations on Electricity made at Philadelphia in America (1751).