ELECTRIC CANNON: This spark eudiometer, circa 1787, is also called a Volta cannon for its inventor. Alessandro Volta (1745–1827) discovered he could fire a cannon that had been corked shut after being filled with methane or a hydrogen-oxygen mixture. A brass-tipped metal rod at the bottom served as a spark plug, which was then sparked from a Leyden jar. It could fire a lead ball 6 meters (20 feet).

















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