DELU'C, JEAN ANDRE, was born at Geneva in 1727. His father, Francois Deluc, was a watch manufacturer, not only skilful in his trade, but conversant with other branches of knowledge, and a writer upon religious and political matters. His son also took part iu the disputes between the n6gatifs and the repr6sentans, or aristocratic and democratio parties, of his native republic, to tho latter of which he belonged ; and' he was scut, in 1768, by his fellow-representatives to Paris to plead their cause with the Duke of Choiseul, the prime Inloister in France.. Ou his return in 1770 ho was made a member of the legislative council; but not long afterwards he left Geneva and its polities for England, to devote himself entirely to scientific) pur suits. lie had from an early age applied himself to the study of geology, and had made excursions into the Alpe, while his brother investigated the mountains of Italy for the same object. His own words best explain his purpose: "My brother and I entered together upon our geological career while I yet lived at Geneva, and after a certain period we came to a first conclusion, which from that time has been our guide, namely, that an essential distinction was to bo made among the various phenomena which the surface of the earth exhibite, with respect to their causes, by determining as to each of them whether the causes which have produced it are still in action, or have, at some epoch, ceased to act. Continuing our observations, wo came at length to a conviction that the formation of our continents, with regard both to their composition and general form, as well as their existence above the level of the sea, should be ascribed to causes no longer in action on our globe, and that the whole of the effects of the still-existing causes Lave been limited to a modification of that original state. After having quitted Geneva, I continued my observa tions In various countries, and more particularly on the sea coast ; my brother likewise pursued his, and we communicated our remarks to each other. I saw the possibility of determining, by the motion of actual cause., what had been the state of on: continents at their birth, and also the possibility of determiniog the time elapsed since that period. I then wrote my first geological work, 'Lettres Physiques et Morales sur l'Ilistoire (19 Is Terre et do l'Homme,' 8vo, La Hive, 1778." Theta letters were addressed to Queen Charlotte, consort of George III., who appointed Delue her reader. They relate only to the Alps of Switzerland ; but In the following year appeared a con tinuation of the work, under the same title, including Deluca's, travels through Rhenish Germany, Hanover, Friesland, Holland, Belgium, &e.,
in 5 thick vole. 8vo. These letters are not merely scientific) treatises; they are also descriptive of scenery, of the Inhabitants, and their manners; they contain etatistical and moral observations, end litany of them are full of interest even to the general reader. One great conclusion which Deluc came to from all his observations was, that the present continents were left dry by a great and sudden revolution of comparatively recent occurrence, not more than four or five thousand years since, which revolution buried under the sea the countries previously iuhabited. This opinion has boon also main. tallied by Saussure, Dolomieu, and for awhile by Cuvier. Deluca agreed with Saussure in considering that the materials which form our mountains were first deposited in horizontal and continuous strata, and that their present broken and dislocated state is the effect of subsequent catastrophes, which however were previous to that which left them dry. Delues whole system concerning the various epochs of the creation corresponding to the six days, or rather periods, of Genesis, appears in several of his numerous works, and especially in his Lettree 06ologiques sur l'Histoitte do In Terre,' addressed to Blumenbach, 1793 ; in his ' Trait6 El6mentaire do Gaologie; 1809, which was also published in English ; and in his ' Geological Travels in the North of Europe and in England,' S vols. Svo, London, 1810. Deluc made also many observations on the atmosphere, and the phenomena of air, beat, and light He wrote Recherches cur les Modifications de ]'Atmosphere, coutenant PHis toire critique du Barometre et du Thermometre, un triad sur Is construction do cee instrumens, dos expdriencee relatives it leura usages, et principalement it la mosuro den hautours, of it in correction des r6fractionn moyennea; avec figures,' 2 vole. 4to, Geneva 1772. It is perhaps in this branch of experimental philosophy that Dolue rendered the most positive services to science. He made groat improvements in the barometer, especially as applied to the measure ment of heights. He also wrote 'Alamein, Bur nn Hygrometre com parable presentd h la Societ6 Royale de Loodres.' Among his other works may be mentioned, ' Idaes sur Is 31ottiorologie, 1786 ; 'Intro duction It la Physique Terrostre par lea Fluidas oxpausibles,' 1803; Traitti El6mentaire cur le Fluide Electro-Galvanique,' 1801.