456 , HENRI VICTOR REGNAULT. 



establishment in Paris ; but after some time was able to enter the 

 Ecole Polytechnique, where he remained two years. After spending 

 eight years in the Department of Mines, he obtained a professor- 

 ship at Lyons, and entered upon the field of research of organic 

 chemistry. The peculiar character of his mind showed itself at once 

 in his new career. He paid no attention to the theories of the day, 

 but worked diligently at the accumulation of materials. A great num- 

 ber of valuable investigations soon followed. Among them, we may 

 notice especially his researches on the action of chlorine upon ether, 

 and upon the chlorides of ethyl and of ethylene ; researches which still 

 retain their value and interest, as the physical properties of the bodies 

 which he obtained were studied with unusual care and thoroughness. 

 In 1840, Regnault was appointed professor in the Ecole Polytechnique, 

 and in 1841 he became Professor of Physics at the College de 

 France. There he began his life-work in physics by a careful and 

 masterly study of the specific heats, first of the elements, and after- 

 ward of compounds. He devised for this study the calorimeter which 

 bears his name, and his results have, to the present day, been standards 

 of accuracy. He established the law of Dulong and Petit for the 

 greater number of the elements, and showed that for many compounds 

 the atomic heat of the whole is the sum of the atomic heat of its con- 

 stituents. He next undertook, by order of the Minister of Public 

 "Works, a series of investigations to determine the principal laws and 

 numerical data which are required in the theory of the steam-engine. 

 Then followed the finest series of experimental determinations of 

 physical constants which has ever been executed by one man, in any 

 age or of any nation. Ten of these memoirs are contained in Volume 

 XXI. of the Memoirs of the Academy of Sciences in Paris, and three 

 others of great length in Volume XXVI. of the same work. These 

 papers, now familiar to all physicists, embrace the following subjects : — 



1. The Expansion of Gases and Dry Vapors, the Coefficients being 

 determined under a Constant Pressure and under a Constant Volume ; 

 at High and at Low Pressures. 



2. The Determination of the Densities of Gases. 



3. The Determination of the Weight of a Litre of Air, and of 

 Nitrogen, Oxygen, Hydrogen, and Carbdnic Dioxide. 



4. On the Measure of Temperatures. 



5. On the Absolute Dilatation of Mercury. 



6. On the Law of the Compressibility of Elastic Fluids. 



7. On the Compressibility of Liquids, and especially that of Mer- 

 cury. 



