Electroscope, condensing

Volta was interested in electricity early in his career. He published his first book on static electricity at the age of twenty-four. In 1775, Volta announced the discovery of the electrophorus, a new sort of instrument that could store static electricity. And in 1782, Volta invented another instrument, the condensing electroscope that was an extremely sensitive measuring device capable of detecting the existence of negative charge in water vapor and in the smoke of burning coals. 

At the end of April, 1800, Sir Joseph Banks showed the first part of Volta s letter to Carlisle, who by 30 April had constructed a pile from 17 silver half-crowns, a like number of pieces of zinc, and pasteboard discs soaked in salt water, arranged in the order silver, zinc, card, silver. . . card, silver, zinc. A gold-leaf condensing electroscope showed that the silver end was negative and the zinc end positive (see p. 14). To ensure better contact, Carlisle put a drop of water on the upper plate and noticed evolution of gas, which Nicholson thought smelt of hydrogen. Nicholson proposed an experiment which they made on 2 May. A joint paper was published by Nicholson in July. ... 

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