The doctrine of 'Specific Heat,' or as it was called by Dr. Black the _capacity_ of bodies for heat, is summed up in the facts, that different bodies contain different quantities of heat in the same bulk or weight; and different quantities of heat are required to raise different bodies to the same sensible temperature. Thus it was found that a pound of gold being heated to 150° and added to a pound of water at 50° the temperature of both became not 100°, the mean between the two but 55°, the gold losing 95° and the water gaining 5°, because the capacity of water for heat is 19 times that of gold. So twice as much heat is required to raise water to any given point of sensible heat as to raise mercury, the volumes of the two fluids compared being equal. The true doctrine of combustion, calcination of metals, and respiration of animals, which Lavoisier deduced from the experiments of Priestly and Scheele upon oxygen gas, and of Cavendish on hydrogen gas, was founded mainly upon the doctrines of latent and specific heat; and it was thus the singular felicity of Black to have furnished both the pillars upon which modern chemistry reposes. In 1766 Black succeeded Dr. Cullen in the professorship of chemistry at the University of Edinburgh, and in the new scene on which he entered his talents became more conspicuously and more extensively useful. Dr. Robison thus characterises him as a lecturer--"He became one of the principal ornaments of the university, his lectures were attended by an audience which continued increasing from year to year; his personal appearance and manners were those of a gentleman, and peculiarly pleasing. His voice in lecturing was low but fine, and his articulation so distinct that he was perfectly well heard by an audience consisting of several hundreds. His discourse was so plain and perspicuous, his illustration by experiment so apposite, that his sentiments on any subject never could be mistaken even by the most illiterate." Dr. Black continued to lecture at the University of Edinburgh for thirty years; he then retired and died three years afterwards, in 1799. His health, never robust, was precarious at all times from a weakness in the bronchia and chest, but he prolonged life by a system of strictest abstinence, frequently subsisting for days together on watergruel and diluted milk. He was never married. He lived in a select circle of friends, the most illustrious men of the times in science and in letters; Watt, Hutton, Hume, Robertson, Smith; and afterwards with the succeeding generation of Scottish worthies, Robison, Playfair, and Stewart. He was extremely averse to publication, contemning the impatience with which so many men of science hurry to the press, often while their speculations are crude and their inquiries not finished. He never published any work himself with the exception of his 'Experiments on Magnesia, &c.,' and two papers, one in the 'London Philosophical