Notices respecting New Books. 43 



that of whioh the object is the absolute dilatation of mercury, 

 and lastly, the memoir on the compressibility of liquids, and in par- 

 ticular of mercury. This last, which contains a detailed explanation 

 of the methods to be employed, does not include a great number of 

 decisive experiments, the author not having had time to execute 

 researches so considerable as the complete study of the subject 

 would have required. One of his pupils, M. Grassi, has lately made 

 known the results he obtained by following the methods indicated 

 by M. Regnault, and by using his apparatus. As to the other two 

 memoirs, they contain important numerical data, it is true, but the 

 interest of these to us, lies essentially in the use which the author 

 makes of them in the more general researches of which we are about 

 to treat. Nevertheless the admirable exactitude of the methods 

 applied by M. Regnault, and the remarkable precision with which he 

 operates, lead us to report here some numerical data, the importance 

 of which will be appreciated by all philosophers, namely, the weight 

 at Paris, that is in the latitude 48° 50' 16", of the litre of air, ni- 

 trogen, oxygen, hydrogen, and carbonic acid, at the temperature of 

 0° Cent, and under the pressure of 0*760 millim., as well as the den- 

 sity of mercury at 0°. 



grm. 



Atmospheric air 1-293187 



Nitrogen gas 1-256167 



Oxygen gas 1 •4-29802 



Hydrogen 0-089578 



Carbonic acid 1 •977414' 



A litre of mercury at 0° C. weighs 13595'93 grms., and a litre of 

 water at the maximum of density 1000*00 grms. Thus the den- 

 sity of mercury is 13*59593; the density of mercury in relation to 

 air, which it is sometimes requisite to know, for instance in the 

 measurement of heights by the barometer, is 10513*5 at the tempe- 

 rature of 0° and under the pressure of 0*760 millim. at Paris. 



The two essential portions of the preliminary researches of M. 

 Regnault are, as we have said, that relative to the laws of dilatation 

 and compressibility of elastic fluids, and that of which the object 

 was the measurement of temperatures. We shall run over them 

 successively, indicating the most striking points. 



JResearc/ies relative to the Laios of Dilatation and Compressibility 

 of Elastic Fluids. 



M. Gay-Lussac, in the first years of this century, at the close of 

 a great number of experiments, came to the determination that the 

 coefficient of dilatation between 0° and 100° C, was the same for all 

 gases, and for vapours when they were at some distance from their 

 point of condensation, and that its value was 0*375. This law and 

 this coefticient, subsequently verified by Dulong and Petit on hy- 

 drogen and atmospheric air between much more distant limits of 

 temperature, were admitted by all physicists and employed in all 

 calculations. Combined with the law equally admitted under the 



