until the late Mr. Bramah, by substituting a pump instead of the
smaller column, converted it into a most valuable and powerful
engine.--The principle of the convertibility of the centres of
oscillation and suspension in the pendulum, discovered by Huygens
more than a century and a half ago, remained, until within these
few years, a sterile, though most elegant proposition; when,
after being hinted at by Prony, and distinctly pointed out by
Bonenberger, it was employed by Captain Kater as the foundation
of a most convenient practical method of determining the length
of the pendulum.--The interval which separated the discovery, by
Dr. Black, of latent heat, from the beautiful and successful
application of it to the steam engine, was comparatively short;
but it required the efforts of two minds; and both were of the
highest order.--The influence of electricity in producing
decompositions, although of inestimable value as an instrument of
discovery in chemical inquiries, can hardly be said to have been
applied to the practical purposes of life, until the same
powerful genius which detected the principle, applied it, by a
singular felicity of reasoning, to arrest the corrosion of the
copper-sheathing of vessels. That admirably connected chain of
reasoning, the truth of which is confirmed by its very failure as
a remedy, will probably at some future day supply, by its
successful application, a new proof of the position we are
endeavouring to establish.

[I am authorised in stating, that this was regarded by Laplace as
the greatest of Sir Humphry Davy's discoveries. It did not fail
in producing the effect foreseen by Sir H. Davy,--the preventing
the corrosion of the copper; but it failed as a cure of the evil,
by producing one of an OPPOSITE character; either by preserving