Dr. Joseph Black was born at Bourdeaux, where his father, a native of Belfast but of Scotch descent, was settled as a wine merchant; and being a man of engaging disposition and extensive information was much esteemed by his friends, among whom he reckoned Montesquieu, at that time one of the presidents of the court of justice in the province where Mr. Black resided. At the age of twelve Joseph Black was sent to a school at Belfast, where he remained for some years. In 1746 he was removed to the College at Glasgow and ever afterwards lived in Scotland, which was, properly speaking, his native country. While at the College of Glasgow he studied under the celebrated Dr. Cullen, then professor of anatomy and lecturer on chemistry, and in the year 1751 removed to Edinburgh to complete the course of his medical studies. In the following year Black made his first great discovery of the cause of the causticity of lime, a property till then supposed to be due to the absorption by the lime of some igneous agency. He placed this question on a scientific basis by ascertaining the chemical difference between quick-lime and other forms of the carbonate, and first announced his discovery in a Latin Thesis upon the occasion of his taking his degree of Doctor of Medicine in 1754. It was not, however, given in its fullest details until the year afterwards, when he published his celebrated work entitled, 'Experiments on Magnesia, Quick-lime, and other alkaline substances;' a work which Lord Brougham describes as being incontestably the most beautiful example of strict inductive investigation since the 'Optics' of Sir Isaac Newton. In 1754, as has been mentioned, Black took his medical degree at Edinburgh; in 1756 he was appointed to succeed Dr. Cullen as professor of anatomy and lecturer on chemistry in the University of Glasgow. Soon after, however, he exchanged this for the professorship of medicine at the same university, as being more congenial to his tastes. Dr. Black continued at the University of Glasgow for the next ten years, and it was during this period, between the years 1759 and 1763, that he brought to maturity his speculations concerning _heat_, which had occupied his attention from the very first commencement of his philosophical investigations. His two great discoveries were the doctrines of 'Latent Heat,' and 'Specific Heat.' The theory of 'Latent' Heat, which mainly urged Watt to the adoption of improved arrangements in the steam-engine, may be briefly described as the absorption of heat by bodies passing from the solid to the fluid state, and from the fluid to the aëriform, the heat having no effect on surrounding bodies (being, therefore, insensible to the hand or thermometer), and only by its absorption maintaining the body in the state which it has assumed, and which it retains until the absorbed heat is given out and has become again sensible, when the state of the body is changed back again from fluid to solid, from aëriform to fluid.