choose those which extend over a space of half a score of years, and
are separated from each other by the gap of a century. Let us, then,
go back a hundred years and examine what would have been the state of
mind of an erudite amateur who had read and understood the chief
publications on physical research between 1800 and 1810.

Let us suppose that this intelligent and attentive spectator witnessed
in 1800 the discovery of the galvanic battery by Volta. He might from
that moment have felt a presentiment that a prodigious transformation
was about to occur in our mode of regarding electrical phenomena.
Brought up in the ideas of Coulomb and Franklin, he might till then
have imagined that electricity had unveiled nearly all its mysteries,
when an entirely original apparatus suddenly gave birth to
applications of the highest interest, and excited the blossoming of
theories of immense philosophical extent.

In the treatises on physics published a little later, we find traces
of the astonishment produced by this sudden revelation of a new world.
"Electricity," wrote the Abbé Haüy, "enriched by the labour of so many
distinguished physicists, seemed to have reached the term when a
science has no further important steps before it, and only leaves to
those who cultivate it the hope of confirming the discoveries of their
predecessors, and of casting a brighter light on the truths revealed.
One would have thought that all researches for diversifying the
results of experiment were exhausted, and that theory itself could
only be augmented by the addition of a greater degree of precision to
the applications of principles already known. While science thus
appeared to be making for repose, the phenomena of the convulsive
movements observed by Galvani in the muscles of a frog when connected
by metal were brought to the attention and astonishment of