Scottish Physician, Chemist, and Inventor. He is remembered for his discoveries of magnesium, latent and specific heat, and carbon dioxide. The son of a wine merchant, he was home schooled until the age of 12, after which he attended grammar school in Belfast, Ireland. In 1746 he entered the University of Glasgow, studying there for four years before spending another four at the University of Edinburgh. Around 1750, while still a student, he developed the analytical balance based on a light-weight beam balanced on a wedge-shaped fulcrum. Each arm carried a pan on which the sample or standard weights was placed. It far exceeded the accuracy of any other balance of the time and became an important scientific instrument in most chemistry laboratories. In 1757 he was appointed Regius Professor of the Practice of Medicine at the University of Glasgow. While there, he discovered that the application of heat to ice at its melting point does not cause a rise in temperature of the ice/water mixture, but rather an increase in the amount of water in the mixture. Additionally, he observed that the application of heat to boiling water does not result in a rise in temperature of a water/steam mixture, but rather an increase in the amount of steam. From these observations, he concluded that the heat applied must have combined with the ice particles and boiling water and become latent. He also explored the properties of a gas produced in various reactions. He found that limestone (calcium carbonate) could be heated or treated with acids to yield a gas he called "fixed air." He observed that the fixed air was denser than air and did not support either flame or animal life, and that when bubbled through an aqueous solution of lime (calcium hydroxide), it would precipitate calcium carbonate. He used this phenomenon to illustrate that carbon dioxide is produced by animal respiration and microbial fermentation. In 1756 he was named Professor of Anatomy and Chemistry at the University of Glasgow and ten years later, the Professor of Medicine and Chemistry at the University of Edinburgh. In November 1783 he became one of the founders of the Royal Society of Edinburgh and from 1788 to 1790 he was President of the Royal College of Physicians of Edinburgh. He was appointed principal physician to British King George III in Scotland. In his later years, his health began to decline, and he died at the age of 71. The chemistry buildings at both the University of Edinburgh and the University of Glasgow are named in his honor.