John André de, a natural philosopher of great merit and celebrity, born at Geneva on the 8th of February 1727, was the son of James Francis de Luc, descended from a family which had emigrated from Lucca and settled at Geneva in the fifteenth century.

His father was the author of some very respectable publications in refutation of Mandeville and other sceptical writers; and he had the means of giving his son an excellent education, although he found it convenient to establish him in a commercial engagement, which principally occupied the first forty-six years of his life, without any other interruption than that which was occasioned by some journeys of business into the neighbouring countries, and a few scientific excursions among the Alps. During these, however, he collected by degrees, in conjunction with his brother William Antony, a splendid museum of mineralogy and of natural history in general; which was afterwards increased by his nephew, André De Luc. He at the same time took his share of the public business of the state, as one of the Council of Two Hundred; and he is still remembered with respect by his fellow-citizens, though he revisited them but once, and that for a few days only, after his emigration, which was the consequence of some unexpected misfortunes in commerce. These he bore with fortitude, and rather rejoiced than lamented at the change in his pursuits, when he removed to England in 1778. He was made a fellow of the Royal Society in the same year, and was appointed reader to the queen; a situation which he continued to hold for forty-four years, and which afforded him both leisure and a competent income. In the latter part of his life he obtained leave to perform several tours in Switzerland, France, Holland, and Germany. In this last-mentioned country he passed six years, from 1798 to 1804; and after his return he undertook a geological tour through England. When he was at Göttingen, in the beginning of his German tour, he received the compliment of being appointed honorary professor of geology in that university; but he never entered upon the active duties of a professorship. He was also a correspondent of the Academy of Sciences at Paris, and a member of several other scientific associations.

His favourite studies were geology and meteorology. The situation of his native country had naturally led him to contemplate the peculiarities of the earth's structure, and the properties of the atmosphere, as particularly displayed in mountainous countries, and as subservient to the measurement of heights. He inherited from his father a sincere veneration for the doctrines of Christianity, and a disposition to defend the Mosaic account of the creation against the prevailing incredulity of the age. His royal patroness was most anxious to encourage and promote his labours in this field; and he is universally allowed to have had great success in removing the specious objections which had been advanced by his antagonists against the comparatively recent formation of the present continents. The testimony of Cuvier is sufficient to establish his character in this capacity, and to place him, at the same time, in the first rank of modern geologists. His original experiments relating to meteorology are, however, not less valuable to the natural philosopher; and he discovered many facts of considerable importance relating to heat and moisture. He noticed the disappearance of heat in the thawing of ice, about the same time that Black founded on it his ingenious hypothesis of latent heat. He ascertained that water was more dense about 40° of Fahrenheit than at the temperature of freezing, expanding equally on each side of the maximum; and he was the original author of the opinion since re-advanced by Mr 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; though it appears difficult to reconcile this opinion with some of the experiments of our author's great rival, Saussure, a philosopher who, as he very candidly allows, made, in many respects, more rapid progress in hygrometry than himself. De Luc's comparative experiments on his own hygrometer and on Saussure's, show only that both are imperfect; but it may be inferred from them, that a mean between both would in general approach much nearer to the natural scale than either taken separately. It appears also probable that Saussure's is rather less injured by time than De Luc's, which has been found to indicate a greater degree of mean moisture every year than the last.

De Luc was a man of warm feelings, and of gentle and obliging manners, fulfilling on all occasions the various duties of a husband, a father, a master, and a friend; at the same time that his literary and scientific merits, and his unremitting attention to the service of the queen, insured her respect and her kindness. He saw her daily for many years, and in his last illness, which was long and painful, she showed him repeated marks of benevolent regard. He died at Windsor on the 7th of November 1817, leaving a variety of works, which will long be remembered in the scientific world.

1. Recherches sur les modifications de l'Atmosphère, 2 vols., 4to, Geneva, 1772; 4 vols., 8vo, Par. 1784. This contains many accurate and ingenious experiments upon moisture, evaporation, and the indications of hygrometers and thermometers, applied to the barometer employed in the measurement of the height of mountains.

2. Relation de différents Voyages dans les Alpes de Faucigny, 12mo, Maastricht, 1771. This relation was written principally by Dentand, who accompanied the two De Luce in these expeditions.

3. Account of a new Hygrometer, Phil. Trans., 1773, p. 404. Like a mercurial thermometer, with an ivory bulb, which expanded by moisture, and caused the mercury to descend.

4. Rules for measuring Heights by the Barometer, Phil. Trans., 1774, p. 158. The first correct rules that had been made public.

5. Barometrical observations on the depth of the mines in the Harz, Phil. Trans., 1777, p. 401. Examples of the application of the rules.

6. An Essay on Pyrometry and Arometry, Phil. Trans., 1778, p. 419. A paper containing many valuable remarks on physical measures in general.

7. Lettres physiques et morales sur l'Histoire de la Terre, 6 vols., 8vo, Hague, 1778. Dedicated to the Queen; relating particularly to the appearance of mountains, and to the antiquity of the human race; explaining the six days of the Mosaic creation as so many periods preceding the epoch of the actual state of the globe; and attributing the deluge to a filling up of cavities supposed to have been left void in the interior of the earth. The whole work is intermixed with interesting observations on men and manners.

8. A second paper concerning some Barometrical Measurements in the Mines of the Harz, Phil. Trans., 1779, p. 485.

9. Lettres sur quelques parties de la Suisse, 8vo, 1781. Also addressed to the Queen.

10. Nouvelles idées sur la Météorologie, 2 vols. in 3, 8vo, Lond. 1787. A very valuable collection of observations and experiments, including some original remarks on electricity.

11. Several papers on Hygrometry, on Vapour, and Rain, on Meteorology in general, on Expansion, and on Refraction, in Koehler's Journal de Physique, XXXVII. XXXVIII. XXXIX. XL. XLII.

12. Some letters on the Physical History of the Earth, in the Monthly Review, enlarged, especially June 1790, and vol. ii. appendix.

13. On Hygrometry, Phil. Trans., 1791, pp. 1, 339. In one of these very important papers the whalebone hygrometer is described.

14. On Evaporation, Phil. Trans., 1792, p. 400. Amongst the fundamental principles laid down in this paper, the independence of vapour and air is asserted.

15. Lettres sur la physique de la Terre, 8vo, Par. 1798. Addressed to Professor Elamendus, and published by Mr Emery, a clergyman at Paris. The substance had already appeared in the Journal de Physique, for 1790, 1791, and 1792. We find in this volume an essay written for a prize at Haarlem in 1791, but without success, on the existence of a General Principle of Morality. It contains an interesting account of some conversations of the author with Voltaire and Rousseau.

16. Lettres sur l'Éducation religieuse de l'Enfance, 8vo, Berlin, 1799.

17. Bacon tel qu'il est, 8vo, Berlin, 1800. Showing the bad faith of the French translator, who had omitted many passages favourable to revealed religion.

18. Précis de la Philosophie de Bacon, 2 vols., 8vo, Paris, 1802. Giving an interesting view of the progress of natural science.

19. Lettres sur le Christianisme, Berlin and Hanover, 1801, 1803. A correspondence with Mr Teller.

20. Introduction à la Physique terrestre par les Fluides expansibles, 8vo, Par., 1803.

21. Traité élémentaire sur le Fluidé Galvanique, 8vo, Paris, 1804.

22. A paper on Lavaux, Journal des Mines, cxv., Nicholson, xx.

23. 24. Several articles in the Brit. Catechist and the Monthly Mag.

25. Traité élémentaire de Géologie, 8vo, Paris, 1809; also in English, by Dolittle, 1810. This little volume is less strictly introductory to geology than the Lettres sur la Terre. It is principally intended as a refutation of the Vulcanian system of Hutton and Playfair, who deduced the changes of the earth's structure from the operation of fire, and attributed a higher antiquity to the present state of the continents than is required in the Neptunian system adopted by De Luc after Dolomieu.

26. He sent to the Royal Society, in 1809, a long paper on separating the chemical from the electrical effects 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, especially with those of the president of the society, that the council probably thought it would be either discouraging error or leading to controversy to admit them into the Transactions. He had, indeed, on other occasions shown somewhat too much scepticism in the rejection of new facts; and he had never been convinced even of Mr Cavendish's all-important discovery of the composition of water. The paper was afterwards published in Nicholson's Journal (xxvi.), and the dry column described in it was constructed by various experimental philosophers. It exhibited a continual vibrating motion, which was made more sensible by the sound of a little bell, struck by the pendulum at each alternation; and the vibration was more or less rapid according to the state of the atmospheric electricity, and according to other circumstances affecting the column; but the motion ceased after a continuance of several months, or perhaps years. There are also papers in volumes xxi. xxii. xxvii. xxviii. xxxi. xxxiii. and xxxv., mostly on electricity and galvanism, together with one on hygrometry, a letter to Rode on comets, and a fanciful theory of the origin of the heat derived from compression. Some of them are dated from Ashfield, near Hemiton, in Devonshire.

27. In the Philosophical Magazine, volumes xxxv. xxxii. and xxxiv., there are also some papers on electricity and geology, especially on that of the Alps, Mount Vesuvius, and of Northumberland; and a note on the sympathetic vibrations of the pendulums of two clocks placed near each other.

28. Geological Travels in the north of Europe, 8vo, Lond. 1810.

29. Geological Travels in England, 2 vols., 8vo, Lond. 1811.

30. Geological Travels in Switzerland and Germany, 2 vols., 8vo, Lond. 1813.

31. An Abridgement of Geology, published in 1817, when he was in his ninetieth year, is mentioned as one of his best works; but it seems to have been only a republication or a translation of some former treatise, perhaps the Traité Élémentaire.

(Philosophical Magazine, November 1817; Monod and Weiss, in the Biographie Universelle, tome xxv., 8vo, Paris, 1820.)