STANHOPE, Charles, third Earl Stanhope (1753–1816), politician & inventor. AL to Mr Cullum. 1815

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STANHOPE, Charles, third Earl Stanhope (1753–1816), politician and inventor. Autograph letter in third person to Mr Cullum [?], 4to, bifolium of 4 sides, Chevening House, near Sevenoaks, Kent, October 15th 1815, in response to his letter regarding the subject of perpetual motion. Stanhope distinguishes two types, the first physical, dependent upon "such alterations in our Atmosphere &c as are capable of being measured by the Barometer, Thermometer, Hygrometer, Pyrometer, Electrometer &c", and the second, mechanical which "has been repeatedly demonstrated to be impossible, and for the following reason. This second sort is founded on the power of Gravity; but the Law respecting it, and which no Man can alter or modify, is this." On this he goes on to explain that "No machine has any tendency to move by Gravity, but so long as the Common Center of Gravity, of all the moving parts of the machine, descends. Now it is perfectly clear, that, whatsoever may be the size of the given piece of mechanism, there is a limit to that size. And, therefore, according to the unalterable law above mentioned, as soon as the said centre of Gravity has arrived at that limit, the tendency of the machine is to stop. It is consequently, as impossible to make a Mechanical Perpetual Motion as to find an odd Number which shall be the sum of two even ones", and he ends upon in explaining a rule for finding the "Common Center of Gravity". The left edge of the front leaf has some adhering brown paper from an album mount (not affecting the text).

Charles, Earl Stanhope made a mark both as a politician and an inventor. He entered politics in 1774, obtained the seat of Chipping Wycombe in 1780, making an immediate impression in the Commons, and in 1786 upon his father’s death succeeded as third Earl Stanhope, remaining active in the Lords right up until 1815 (the time of this letter). Throughout his political career Stanhope took an active interest in several branches of science. He had studied mathematics at the University of Geneva, was elected a fellow of the Royal Society in 1772, and went on to devote a large part of his income to experiments in science and philosophy. He studied electricity, publishing the Principles of Electricity in 1779 which contained the rudiments of his theory on the "return stroke" resulting from the contact with the earth of the electric current of lightning, which were afterwards amplified in a paper to the Philosophical Transactions in 1787. His inventions include the printing press and the lens which bear his name; a monochord for tuning musical instruments; and he devised two calculating machines. He consulted Boulton and Watt over developing steam-powered propulsion; registered patents for steamships in 1790 and in 1807; and suggested improvements in canal locks.