| About 1791-92 Luigi Galvani (1737-98), a biologist
and professor at the University of Bologna, noticed that frogs' legs, impaled
on brass hooks, contracted when the legs came in contact with an iron lattice.
Unfortunately, he made the assumption that the source of the effect was
in the animal tissue.
In the last years of the 18th century Alessandro Volta (1745-1827) of the University of Pavia showed that any moist, porous material between two dissimilar metals would produce the same effect.
|In the Pile that Volta described in 1800, a disk of copper is placed
at the bottom, followed by a disk of cloth soaked in brine or acidulated
water, followed by a disk of zinc. More sets of copper-cloth-zinc disks
is placed on top, until the pile reaches a height of about 30 cm. The positive
end of the pile is the bottom copper disk, and the negative end is the
top zinc disk. The three glass rods serve to confine the disks into a vertical
An alternative arrangement of the metallic disks is Volta's Crown of Cups.
The voltaic pile at the left, in the collection at Dartmouth College in Hannover, New Hampshire, is unusual in its provision of a built-in spark gap.
Cells, which were developed from Volta's basic idea of dissimilar
metals separated by an electrolyte, were developed in the first half of
the 19th century.