is the birthday of Alessandro Volta, an Italian physicist born in 1745 who discovered how to produce electric current. It was known that muscles in dead frogs contract when two dissimilar metals (brass and iron) are put in contact with one another and the muscle. Volta proposed that the source of the electricity was not the animal tissue but rather the junction of the metals, and he made a list that ranked metals according to the strength of the sensation they produced on his tongue. By 1800, Volta discovered how to create high electric currents, using two arrangements of conductors: one a pile of silver and zinc discs separated by cardboard moistened with brine; the other a series of glasses containing saltwater and connected with bimetallic, curved electrodes. This paved the way for discoveries about electromagnetism and the invention of electrical machines. The unit of electric potential, the volt, is named in his honor.
[Source: Roy Porter, Ed., The Biographical Dictionary of Scientists (Oxford University Press, ed. 2, 1994).]