.a work due from the Roman school, despatched from Tangiers the large canvas, Execution without Hearing under the Moorish Kings, in which the painter had played with the blood of the victim as were he a jeweller toying with rubies. The war arose, and found Régnault foremost in the devoted ranks of Buzenval, where he fell on January 19, 1871.

See Correspondance de II. Régnault ; Duparc, II. Régnault, sa vie et son oeuvre ; Cazalis, H. Régnault, 1843-1871 ; Baillière, Les artistes de mon temps; C. Blanc, H. Régnault; P. Mantz, Gazette du Beaux Arts, 1872.

REGNAULTHenri Victor (1811-1878), was born on July 21, 1811, at Aix-la-Chapelle. His early life was a struggle with poverty. When a boy he went to Paris, and after a time succeeded in obtaining a situation in a large drapery establishment, where he remained, occupying every spare hour in study, until he was in his twentieth year. Then he entered the École Polytechnique, and, after making the best use of his increased opportunities, passed in 1832 to the Ecole des Mines, where he developed an aptitude for experimental chemistry.

A few years later he was appointed to a professorship of chemistry at Lyons, and devoted himself to research amongst organic compounds. He paid little attention to theories and cared only for facts; but, by his unequivocal proof of the substitution of chlorine for hydrogen in hydrocarbons, he greatly assisted his countrymen Laurent and Dumas in establishing the type-theory of organic compounds. Regnault’s most important chemical work was a series of researches, commenced in 1835, on the haloid and other derivatives of unsaturated hydrocarbons. This made him the discoverer of the vinyl group of compounds, carbon tetrachloride (CC1 4 ), and of perchlorether (C 4 Cl 10 O). He studied many of the natural alkaloids and organic acids, introduced a classification of the metals according to the facility with which they or their sulphides are oxidized by steam at high temperatures, and effected a comparison of the chemical composition of atmospheric air from all parts of the world.

In 1840 Régnault was recalled to Paris by his appointment to the chair of chemistry in the École Polytechnique; at the same time he was elected a member of the Académie des Sciences, in the chemical section, in room of M. Robiquet; and in the following year he became professor of physics in the Collège de Prance, there succeeding Dulong, his old master, and in many respects his model. From this time Régnault devoted almost all his attention to practical physics; but in 1847 he published a four-volume treatise on Chemistry which was highly esteemed and has been translated into many languages.

Régnault is perhaps best known by his careful redetermination of the specific heats of all the elements obtainable, and of many compounds—solids, liquids, and gases—by which he was enabled to correct the values obtained by Dulong and Petit, and to reduce the number of exceptions to their law that the specific heat of an element varies inversely as its atomic weight , and of a compound as its molecular weight. He investigated the expansibility of gases by heat, determined the coefficient for air as 003663־, and showed that, contrary to previous opinion, no two gases had precisely the same rate of expansion. By numerous delicate experiments he proved Boyle’s law that the volume of a gas is inversely as the pressure it supports to be only approximately true, and that those gases which are most readily liquefied diverge most widely from obedience to the law. Régnault studied the whole subject of thermometry critically; he introduced the use of an accurate air-thermometer, and compared its indications with those of a mercurial thermometer, determining the absolute dilatation of mercury by heat as a step in the process. He also paid attention to hygrometry and devised a hygrometer in which a cooled metal surface is used for the deposition of moisture.

In 1854 he was appointed to succeed Ebelman as director of the celebrated porcelain manufactory at Sèvres. He carried on the great research on the expansion of gases in the laboratory at Sèvres, but all the results of his latest work were destroyed during the Franco-German War, in which also his son Henri (noticed above) was killed. Régnault never recovered the double blow, and, although he lived until January 19, 1878, his scientific labours ended in 1872. He wrote more than eighty papers on scientific subjects, and he made fine researches, many of them of importance, in conjunction with other workers. His greatest work, bearing on the practical treatment of steam-engines, forms vol. xxi. of the Mémoires de l'Académie des Sciences.

Régnault was great as a laborious worker; in all his researches he overcame every difficulty by his determined perseverance, his unusual natural ingenuity in devising apparatus, and his rare power of manipulation. Although few discoveries are associated with his name, the mass of physical constants which he determined with the utmost accuracy constitutes a powerful instrument of further advance, and the thorough training which he gave his students has provided many painstaking and exact workers in the field of physics.

REGNAULTJean Baptiste, French painter, was born at Paris on 9th October 1754, and died in the same city on November 12, 1829. He began life at sea in a merchant vessel, but at the age of fifteen his talent attracted attention and he was sent to Italy by M. de Monval under the care of Bardin. After his return to Paris, Régnault, in 1776, obtained the Great Prize, andin 1783 he was elected Academician. His diploma picture, the Education of Achilles by Chiron, is now in the Louvre, as also the Christ taken down from the Cross, originally executed for the royal chapel at Fontainebleau, and two minor works— the Origin of Painting and Pygmalion praying Venus to give Life to his Statue. Besides various small pictures and allegorical subjects, Régnault was also the author of many large historical paintings; and his school, which reckoned amongst its chief attendants Guérin, Crepin, Lafitte, Blondel, Robert Lefevre, and Menjaud, was for a long while the rival in influence of that of David.