ingenious mechanical devices in
all branches of science and mechanics. It was he who made the famous
air-pump of Robert Boyle, based on Boyle's plans. Incidentally, Hooke
claimed to be the inventor of the first air-pump himself, although this
claim is now entirely discredited.

Within a period of two years he devised no less than thirty different
methods of flying, all of which, of course, came to nothing, but go to
show the fertile imagination of the man, and his tireless energy. He
experimented with electricity and made some novel suggestions upon the
difference between the electric spark and the glow, although on the
whole his contributions in this field are unimportant. He also first
pointed out that the motions of the heavenly bodies must be looked upon
as a mechanical problem, and was almost within grasping distance of the
exact theory of gravitation, himself originating the idea of making use
of the pendulum in measuring gravity. Likewise, he first proposed the
wave theory of light; although it was Huygens who established it on its
present foundation.

Hooke published, among other things, a book of plates and descriptions
of his Microscopical Observations, which gives an idea of the advance
that had already been made in microscopy in his time. Two of these
plates are given here, which, even in this age of microscopy, are
both interesting and instructive. These plates are made from prints of
Hooke's original copper plates, and show that excellent lenses were
made even at that time. They illustrate, also, how much might have been
accomplished in the field of medicine if more attention had been given
to microscopy by physicians. Even a century later, had physicians made
better use of their microscopes, they could hardly have overlooked such
an easily found parasite as the itch mite, which is quite as easily
detected as the cheese mite, pictured in Hooke's book.

In justice to Hooke, and in extenuation of his otherwise inexcusable
peculiarities of mind, it should be remembered that for many years he
suffered from a painful and wasting disease. This may have affected his
mental equilibrium, without appreciably affecting his ingenuity. In his
own time this condition would hardly have been considered a disease; but
to-day, with our advanced ideas as to mental diseases, we should be more
inclined to ascribe his unfortunate attitude of mind to a pathological
condition, rather than to any manifestation of normal mentali