made by him one hundred and fifty years ago, is
still in use and could hardly now be surpassed in substantial
excellence. The mural arch in the same establishment, used for the
testing of quadrants and other marine instruments, was also his work.
When the French government sent Maupertuis within the polar circle, to
ascertain the exact figure of the earth, it was George Graham,
Clock-maker of Fleet Street, who supplied the requisite instruments.

But it was not his excellence as a mechanic that causes his name to be
remembered at the present time. He made two capital inventions in
clock-machinery which are still universally used, and will probably
never be superseded. It was a common complaint among clock-makers, when
he was a young man, that the pendulum varied in length according to the
temperature, and consequently caused the clock to go too slowly in hot
weather, and too fast in cold. Thus, if a clock went correctly at a
temperature of sixty degrees, it would lose three seconds a day if the
temperature rose to seventy, and three more seconds a day for every
additional ten degrees of heat. Graham first endeavored to rectify this
inconvenience by making the pendulum of several different kinds of
metal, which was a partial remedy. But the invention by which he
overcame the difficulty completely, consisted in employing a column of
mercury as the "bob" of the pendulum. The hot weather, which lengthened
the steel rods, raised the column of mercury, and so brought the centre
of oscillation higher. If the column of mercury was of the right length,
the lengthening or the shortening of the pendulum was exactly
counterbalanced, and the variation of the clock, through changes of the
temperature, almost annihilated.

This was a truly exquisite invention. The clock he himself made on this
plan for Greenwich, after being in use a century and a half, requires
attention not oftener than once in fifteen months. Some important
discoveries in astronomy are due to the exactness with which Graham's
clock measures time. He also invented what is called the "dead
escapement," still used, I believe, in all clocks and watches, from the
commonest five-dollar watch to the most elaborate and costly regulator.
Another pretty invention of his was a machine for showing the position
and motions of the heavenly bodies, which was exceedingly admired by our
grandfathers. Lord Orrery having amused himself by copying this machine,
a French traveler who