The latter had then at his
disposal nothing but a relatively weak pile, and it is very natural
that, under such circumstances, he produced a spark without observing
its properties as a light producer.
It was only in 1808 that he was in a position to operate upon a larger
scale. At this epoch a group of men who were interested in the progress
of science subscribed the necessary funds for the construction of a
large battery designed for the laboratory of the Royal Institution. This
pile was composed of 2,000 elements mounted in two hundred porcelain
troughs, one of which is still to be seen at the Royal Institution. The
zinc plates of these elements were each of them 32 inches square, and
formed altogether a surface of 80 square meters. It was with this
powerful battery that Davy, in 1810, performed the experiment on the
voltaic arc before the members of the Royal Institution.
The carbons employed were rods of charcoal, and were rapidly used up
in burning in the air. So in order to give longer duration to his
experiment, Davy was obliged, on repeating it, to inclose the carbons in
a glass globe like that used in the apparatus called the electric egg.
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