NICOLAS FRANÇOIS, is justly reckoned among the most distinguished of the chemists and natural philosophers of the age. He was born at St Leonard (Haute-Vienne), December 6, 1778, and was educated at L'École Polytechnique, where he attracted the attention of Berthollet; and from thence he passed to L'École des Ponts et Chaussées.

The expansion of gases had long been a subject of investigation among the savans of his day; and though the young Gay-Lussac was as yet but on the threshold of the temple of science, he set his heart upon resolving the important problem. The result of his experiments was, that the difference of the proportions hitherto obtained was owing to the presence of water in the gases, and that when perfectly free from moisture they all dilate uniformly with every degree of increased heat. By further experiments on mercury he ascertained that it dilates equably from the temperature of ice (32° Fahr.) to that of boiling water (212° Fahr.), and that at the same time it increases one-third in volume.

Intimately connected with the expansion of gases was that of balloons, to which Gay-Lussac's attention was particularly directed by some observations of the natural philosopher Charles, who remarked what important experiments in magnetism, electricity, and atmospheric phenomena might be made in the higher regions of the atmosphere by means of balloons. See AERONAUTICS, vol. ii., p. 181.

The services which Gay-Lussac had thus rendered to science were rewarded by the general esteem of the eminent men of the day, and especially by the friendship of Alexander von Humboldt, in company with whom he made a tour through France, Switzerland, Italy, and Germany, in the years 1805 and 1806, taking magnetic observations at various stations between the latitudes of Naples and Berlin, with a view to determine the position of the magnetic equator, and its intersection with the terrestrial equator. One result, among other important discoveries, was that the great chains of mountains, and even volcanoes, have no perceptible influence on the magnetic force, and that it diminishes in proportion to the distance from the terrestrial equator.

Another important class of Gay-Lussac's experiments was in connection with the voltaic or galvanic pile. He missed, indeed, the reward promised by Napoleon for the most important discoveries obtained by means of this apparatus, the French Institute having decreed it to Sir Humphry Davy, who by its use discovered potassium and sodium, demonstrating that the two substances called potass and soda are not simple bodies, but combinations of oxygen, with a metallic base. These researches, however, the French philosopher had the merit of following up. The Institute having provided the means of constructing a battery for operations on a great scale, appointed Gay-Lussac and Thénard to preside over the experiments for which the battery was designed. In 1811 these able chemists published, in two 8vo volumes, and under the title of Recherches physico-chimiques, the experiments of several years. The results appear chiefly to have been the obtaining of potassium and sodium in greater proportions than those men- tioned by Sir H. Davy; the decomposition of alkalies by fire at a high temperature; the separation of boron from boric acid; the analysis of organic products by their combustion by means of chlorate of potass; and finally, they demonstrated that sugar, starch, and wood contain nearly the same proportions of hydrogen and oxygen as water.

Gay-Lussac published his curious researches on the theory of vapours and capillary attraction; on the expansion of gases; on the nature of chloric and hydrosulphuric acids; his observations on the number and nature of metallic oxides; and his experiments on cyanogen and iodine in the Annales de Chimie et de Physique, which he edited in concert with Arago; Le Bulletin de la Société Philomathique; and Les Mémoires de la Société d'Arcueil, which was partly edited by Humboldt.

Few men have led such a life of scientific industry as Gay-Lussac. There is scarcely a branch of chemical or physical science to which he did not contribute some important discovery. Among these, his discovery of the general laws in the composition of bodies, particularly in the animal and vegetable kingdoms, may be considered the most distinguished. He was an able and ingenious manipulator, and it would be impossible to recapitulate in a brief memoir a tithe of his philosophical labours, and their important bearings on the progress of natural science. In 1808 he became a member of the Académie des Sciences; in 1816, professor of chemistry at the Jardin du Roi and L'École Polytechnique; and there were few learned societies in France or elsewhere of which he was not a member.

In 1831, being elected deputy for his native department, La Haute-Vienne, Gay-Lussac was called to a new sphere of duty. It would seem that he had never studied the higher questions of legislation and government, or attached himself to any political creed; but he took part in discussions relative to industrial matters, to commerce, to public instruction, and to various educational establishments. After the dissolution of the government in 1837, he was re-elected to the same office, but missed his election in 1839. Immediately after this disappointment he was elevated to the dignity of a peer of France, by an ordonnance of the king, dated March 1839.

After a long life thus devoted to the interests of science, Gay-Lussac died at his residence in the Jardin des Plantes of Paris, May 9, 1850, in the 72d year of his age. (a. v. v.)