54) Notices respecting New Books. 



forces be at the same time as great as possible ; conditions which 

 are opposed to each other, except by bringing the temperature into 

 action. Then the special nature of the atoms no longer interposes 

 in the phaenomena, and the laws exhibit a generality which they did 

 not possess when, the atoms being more closely approximated, their 

 mutual action influenced the result. Thus hydrogen presents the 

 same coefficient of dilatation under different pressures, and the other 

 gases come nearer to having the same coefficient in proportion as 

 their density is less. With regard to that aberration from Mariotte's 

 law, in a contrary direction from other gases, presented by hydrogen, 

 and which the other gases would probably present at high tempera- 

 tures, it would be a general consequence, and therefore similar for 

 all elastic fluids, of the laws which regulate the constituent elastic 

 force of the gas ; it would simply prove that the intensity of this 

 force is not so simple a function as has been supposed, of the di- 

 stance which separates the atoms. 



Finally, we will remark, that these considerations, based on the 

 experimental researches of M. Regnault, are very contrary to the 

 opinion long received, that under the same pressure and at the same 

 temperature, equal volumes of all gases contain the same number of 

 atoms. They are of a nature, on the other hand, to lead to the pre- 

 sumption, that the densities of gases do not at all express the rela- 

 tions which exist between their atomic weights ; conclusions, more- 

 over, which purely chemical considerations tend to corroborate, and 

 at which I had already arrived in 18335 when drawing up a report 

 on the Traite de Chimie of Berzelius. 



The alteration produced in the chemical properties of gases by 

 their less or greater degree of density, is another proof to be added 

 to those I have already indicated, that elastic fluids have an indi- 

 vidual molecular constitution ; a kind of cohesion, as it were, when 

 their atoms are not removed beyond a certain limited distance from 

 each other. This interesting and delicate subject, which I have but 

 just touched upon, can only be treated properly when new facts shall 

 have been added to those which the sagacity and perseverance of 

 physicists like M. Regnault have enriched it. I therefore terminate 

 here the report of this portion of the researches of the French phi- 

 losopher, and now enter upon the memoir in which he treats of the 

 m,easurement of temperatures. 



The Measurement of Temperatures. 



This subject, which seemed to have been exhausted by MM. Du- 

 long and Petit, in their excellent investigations made thirty years 

 ago, has been wholly worked over again by M. Regnault, this re- 

 vision having been rendered necessary from the circumstance that, 

 by his own experiments, the French physicist had so importantly 

 modified the data on the dilatation and compressibility of gases pre- 

 viously received. 



The problem of the measurement of temperatures is perhaps 

 the most difficult of solution that physics present. We have, in- 

 deed, no direct means of measuring the quantities of heat absorbed 



