Jean André Deluc (8.02.1727-7.11.1817) was a Swiss physicist. He was born in Geneva. He took an active part in political life. After 1770 he left Geneva and took up physics and geology. He travelled, then was reader to the English queen, and from 1798 (for a short time) was professor at the University of Göttingen. From 1808 he lived in England.
His research concerned molecular physics, heat, electricity and optics. He studied the expansion of liquids and of air, the processes of evaporation, melting and boiling, and latent heat. In 1754—55 he showed that the temperature does not change while ice melts and that additional heat is required for its passage into water. He found anomalies in the thermal expansion of water, in particular that water has its maximum density not at the freezing temperature but at 4°C (1772). He was the first to introduce a temperature correction to the readings of the barometer (the Deluc barometric correction), gave a formula for it and drew up a table. He used the barometer to measure altitude and proposed the siphon barometer. He built (1781) a hygrometer of whalebone (the Deluc hygrometer) and improved it in 1787. He determined the coefficient of expansion of air. He developed theories of electricity (1787) and of heat. He invented the dry cell.
A Fellow of the Royal Society (1773) and a member of the Paris Academy of Sciences (1803).