# Dictionary of National Biography, 1885-1900/Deluc, Jean André

​DELUC, JEAN ANDRÉ (1727–1817), geologist and meteorologist, was born at Geneva on 8 Feb. 1727. He came of a family which had resided in Geneva for about three centuries, having originally been natives of Lucca. Deluc was well educated by his father, François Deluc, and early showed a special bent for mathematics and natural science. François Deluc had published several writings in opposition to the doctrines of Mandeville and other rationalistic writers, and carefully trained his children in his own views. Deluc became a prominent merchant and politician in Geneva. In 1768 he headed a successful embassy to Paris, and two years later he was chosen a member of the council of two hundred. Scientific studies occupied his spare moments, and, in company with his brother Guillaume Antoine, he visited almost every tract of the Alps, forming extensive collections of rocks, minerals, &c., which he ultimately presented to his nephew, André Deluc, by whom they were largely augmented.
In 1773 the business house of which Deluc was the head failed, and he settled in England. He was warmly received, elected a fellow of the Royal Society, and soon afterwards appointed reader to Queen Charlotte, consort of George III, a post which he held until his death. It afforded him a competent income, with the opportunity to devote himself wholly to scientific research. Having to be in almost daily attendance on the queen, he took up his residence at Windsor. He is occasionally mentioned in Madame d'Arblay's ‘Diary.’ In 1798 Deluc obtained leave to make an extended tour on the continent. He visited France, Switzerland, Holland, and Germany, everywhere studying the rocks of those countries, and discussing their nature with local students of geology. At the university of Göttingen Deluc was elected honorary professor of geology in 1798; he was also made correspondent of the Academy of Sciences at Paris, and received several similar honours. Returning to England in 1804, Deluc made an extended journey over Great Britain, diligently noting the geological phenomena he met with.
From this period until his death, 7 Nov. 1817, Deluc resided at Windsor. For the last few years of his life he was confined to his house by illness, but was still engaged in composition. His last illness was a painful and lingering one.
It is difficult now to estimate at its right value Deluc's work in geology. Cuvier thought highly of him. The great object of his work among the rocks was to reconcile science with the record in Genesis. He tried, like later writers, to show that the six ‘days’ correspond with six actual ‘periods’ of indefinite duration. His theory led him to argue that the existing continents are of no ​great antiquity, and accordingly he advocated the Neptunian system of Dolomieu in preference to the Vulcanian system of Hutton and Playfair. He explained the deluge as due to the filling up of enormous cavities in the interior of the earth. Throughout his life Deluc maintained a correspondence with the leading philosophers of the continent. Some of his controversies—as those with Professor Blumenbach and Dr. Teller of Berlin—were conducted by means of a long series of letters contributed to the ‘Journal de Physique.’ He was an ardent admirer of Bacon, and published one work containing an abstract of Bacon's reasoning, and another (‘Bacon tel qu'il est’) showing how a French translator had wilfully omitted several parts of Bacon's writings which were favourable to revealed religion.
Deluc made very numerous experiments on the atmosphere, inquiring into the modes of production of clouds, rain, hail, dew, &c. He was one of the first to notice that when ice thaws there is a disappearance of heat. In Deluc's time this was considered a great mystery, until Dr. Black founded on it his theory of ‘latent’ heat. Deluc also proved that water attains its maximum density at a temperature of 39 degrees. He enunciated a point of the highest importance when he endeavoured to show that the amount of water-vapour in the atmosphere, or in any closed vessel, is independent of the density of the air or any other gaseous substance in which it is diffused, a theory which was subsequently proved more clearly by John Dalton. Deluc invented a hygrometer, consisting of an ivory bulb filled with mercury and provided with a glass stem, like an ordinary thermometer. The ivory expanded or contracted in accordance with the amount of water-vapour present in the air, and the mercury showed this contraction or expansion by moving up or down the tube. Deluc also investigated the effects of heat and pressure upon the mercurial barometer; and the first correct rules ever published for measuring the heights of mountains by the barometer are contained in a paper which he contributed to the ‘Philosophical Transactions’ for 1771.
His chief discovery was his ‘Dry Pile’ or ‘Electric Column,’ which he published in ‘Nicholson's Journal’ 1810. It consisted of a great number of discs of zinc-foil, and of paper silvered on one side only. These discs were arranged one upon the other in the following order, zinc, silver, paper, to the number of some hundreds or even thousands; they were placed within a glass tube and firmly screwed together. When the uppermost silver was then connected by a wire with the lowest zinc disc, a current of electricity was found to pass along the wire. Such dry piles retain the power of producing electricity for very long periods, and there is one in the Clarendon Laboratory at Oxford which has been continuously in action, ringing ten small bells, for over forty years. Deluc's dry pile was subsequently improved by Zamboni, after whom it is therefore sometimes called, but the whole credit of its invention belongs to Deluc. Deluc was very sceptical as to newly advanced theories. He never accepted Cavendish's proof of the decomposition of water. He consequently combated Lavoisier's chemical theory, which relied on the compound nature of water for one of its fundamental proofs. He was soon left in a minority.
Deluc's works are: 1. ‘Recherches sur les Modifications de l'Atmosphere,’ 2 vols. 4to, Geneva, 1772; and 4 vols. 8vo, Paris, 1784. 2. ‘Lettres sur l'Histoire Physique de la Terre,’ 8vo, Paris, 1798; abridged translation into English by Delafite, 1 vol. 1831. 3. ‘Bacon tel qu'il est,’ 8vo, Berlin, 1800. 4. ‘Précis de la Philosophie de Bacon,’ 2 vols. 8vo, Paris, 1802. 5. ‘Lettres sur le Christianisme,’ Berlin and Hanover, 1801–3. 6. ‘Traité Elémentaire de Géologie,’ 8vo, Paris, 1809; translated into English by the Rev. H. Delafite same year. 7. ‘Geological Travels in the North of Europe and in England,’ 3 vols. 1810. 8. ‘Geological Travels in some parts of France, Switzerland, and Germany,’ 1803. 9. ‘Traité Elémentaire sur le Fluide Electrico-galvanique,’ 2 vols. 1804. 10. ‘Idées sur la Météorologie,’ 2 vols. in 3, 1786. 11. ‘Lettres sur l'Education Religieuse de l'Enfance,’ 1799. 12. ‘Introduction à la Physique Terrestre par les Fluides expansibles,’ 2 vols. 1803. 13. ‘Lettres sur l'Histoire de la Terre et de l'Homme,’ 5 vols. 8vo, 1779. In addition to the books named above, Deluc was the author of numerous papers on scientific subjects which appeared in ‘Nicholson's Journal,’ the ‘Philosophical Magazine,’ the ‘Philosophical Transactions,’ ‘Journal des Sçavans,’ ‘Monthly Review,’ ‘British Critic,’ the ‘Monthly Magazine,’ &c.
W. J. H.