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 He made two capital inventions in clock-machinery which are still universally used, and will probably never be superseded.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 saw it complimented the maker by naming it an Orrery, which has led many to suppose it to have been an invention of that lord. It now appears, however, that the true inventor was the Fleet Street clock-maker. The merits of this admirable mechanic procured for him, while he was still little more than a young man, the honor of being elected a member of the Royal Society, the most illustrious scientific body in the world. And a very worthy member he proved. If the reader will turn to the Transactions of that learned society, he may find in them twenty-one papers contributed by George Graham. He was, however, far from regarding himself as a philosopher, but to the end of his days always styled himself a clock-maker. They still relate an anecdote showing the confidence he had in his work. A gentleman who bought a watch of him just before departing for India, asked him how far he could depend on its keeping the correct time.