DELUC, JEAN ANDRE (17 2 ), Swiss geologist and meteorologist, was born at Geneva on Feb. 8, 1727, and spent his early manhood in business and politics in his native city. He settled in England in 17 73, and became reader to Queen Charlotte, a position which gave him a competency and leisure to travel in pursuit of his scientific studies. Deluc, who was a fellow of the Royal Society, died at Windsor on Nov. 7, 1817.
His principal geological work, Lettres physiques et morales sur les montagnes et sur l'histoire de la terre et de l'homme (17 78 ; enl. ed. 1779), explained the six days of the Mosaic creation as so many epochs preceding the actual state of the globe. Deluc discovered many important facts relating to heat and moisture. He noticed the disappearance of heat in the thawing of ice about the same time that J. Black founded on it his ingenious hypothesis of latent heat. He ascertained that water was more dense about 40° F (4° C) than at the temperature of freezing, expanding equally on each side of the maximum ; and he was the originator of the theory, readvanced later by Dalton, that the quantity of aqueous vapour contained in any space is independent of the presence or density of the air, or of any other elastic fluid.
In the Phil. Trans., 1773, appeared his account of a new hy grometer, which resembled a mercurial thermometer, with an ivory bulb, which expanded by moisture, and caused the mercury to descend. The first correct rules ever published for measuring heights by the barometer were those he gave in the Phil. Trans., 1771, p. 158. He sent to the Royal Society, in 1809, a long paper on separating the chemical from the electrical effect of the pile, with a description of the electric column and aerial electroscope, in which he advanced opinions so little in unison with the latest discoveries of the day, that the council deemed it inexpedient to admit them to the Transactions. The paper was afterwards pub lished in Nicholson's Journal (xxvi.), and the dry column de scribed in it was constructed by various experimental philosophers. This dry pile or electric column has been regarded as his chief discovery.