4ii Notices respectijig New Books. 



name of Mariotte's law, that the densities of air at equal temperature 

 are proportional to the pressures, the law of Gay-Lussac furnished 

 to geometers, and in particular to Laplace, the means of arriving by 

 calculation at simple and general notions on the constitution of 

 elastic fluids. It was believed that thus was found, in the gaseous 

 state, the state of matter most fitted to bring to light the general 

 qualities of bodies, since it was independent of the special nature of 

 each of them. 



Already, it must be remembered, the researches of Dulong and 

 Petit, on the cooling of bodies in different gases, had revealed a 

 special influence independent of the density and the other general 

 conditions of elastic fluids, and proper to each in particular. After 

 the experiments of Faraday on the liquefaction of gases, several 

 physicists, and particularly MM. CErsted and Svendsen in 1826, and 

 M. Despretz in 1827, perceived that several gases compared with 

 atmospheric air, departed from the law of Mariotte, and presented 

 compressibilities increasing with the pressure, even from the point 

 of two atmospheres. Some uncertainty was equally manifested re- 

 specting Mariotte's law, applied to atmospheric air, but they appeared 

 to vanish completely after the excellent researches of MM. Arago and 

 Dulong, executed in 1827 at the request of the Academy of Sci- 

 ences of Paris, researches which caused the law of the compres- 

 sibility of atmospheric air to be regarded as directly verified up to 

 twenty-seven atmospheres, and capable of being extended without any 

 notable error much beyond this limit. M. Pouillet announced lately 

 that he had ascertained that oxygen, nitrogen, hydrogen, binoxideof 

 nitrogen, and carbonic oxide follow, up to 100 atmospheres, the same 

 law of compression as atmospheric air. We shall see that these re- 

 sults, and that of MM. Arago and Dulong, must only be admitted 

 with some reservation, and that M Regnault has demonstrated by 

 direct methods that they are not rigorously exact, after having al- 

 ready remarked that they were not readily reconcileable with his 

 experiments on the dilatation of gases. We will therefore in the 

 first place say a few words on this subject. 



The coefficient of Gay-Lussac had been generally admitted for a 

 great number of years, when a Swedish physicist, M. Rudberg, threw 

 doubts on its exactitude, showing by a series of experiments care- 

 fully made, that it was too high, and that its true value should be 

 comprehended between 0"364? and 0*365. 



M. Regnault, considering that new experiments were necessary to 

 remove all the doubts in this respect, gave himself up ardently to 

 them, at the time when M. Magnus was making analogous researches 

 in Berlin. 



Five series of experiments were made on atmospheric air ; in the 

 four first, which only differed from each other in the methods em- 

 ployed, and were based on the same principle, the dilatation of the 

 gas was determined in an indirect manner. Direct measurement 

 was made of the increase of elastic force which the gas, brought into 

 a volume sensibly constant, received through the elevation of the 

 temperature, and the dilatation was concluded, by making use of 



