M. Achille Cazin on Internal Work in Gases, 83 



Many experimental researches have been made on this subject ; 

 but, whether because they have led us to regard the internal 

 work of gases as very slight, or because they have not appeared 

 sufficiently conclusive, several authors who have developed the 

 mechanical theory of heat have only applied its principles to an 

 ideal gaseous state, defined by the complete absence of all in- 

 ternal work, or else, under another form, by the laws of Mariotte 

 and Gay-Lussac. Hence it follows that the formulae given for 

 gases are far from representing the real phenomena, and that it 

 is frequently difficult to appreciate the degree of approximation 

 which their use admits of. This is not of much importance in 

 technical applications; but from a speculative point of view I 

 think it is very important to abandon altogether formulae the 

 inexactness of which is certain. 



I will endeavour briefly to recall the facts upon which the no- 

 tion of internal work in gases is based. 



When we apply the principles of the mechanical theory of heat 

 to gases assuming that internal work is never produced, we de- 

 monstrate that the gas follows the laws of Mariotte and Gay- 

 Lussac*. Now the two fundamental principles of this theory 

 are: — 



1. The principle of the equivalence of heat and work, indicated 

 for the first time, in France, by M. Marc Seguinf, developed by 

 Dr. Mayer in Germany J, and demonstrated experimentally first 

 by Mr. Joule in England (1843), then by a great number of 

 French and other physicists : this principle cannot now be 

 doubted, and the divergencies of opinion relate only to the nu- 

 merical value of the ratio of equivalence. 



2. A principle conceived by Sadi Carnot (1824) at a time 

 when the preceding principle was unknown, and which was 

 afterwards rectified by Sir W. Thomson in England (1849), and 

 Clausius in Germany (1850). This latter principle has gene- 

 rally been regarded as distinct from the first ; not being capable 

 of a direct experimental verification, it constituted a kind of pos- 

 tulate the correctness of which was demonstrated by the expe- 

 rimental verification of all its consequences. M. Clausius has 

 in fact demonstrated it by combining the principle of equivalence 

 with the following principle, which he has assumed as an axiom : — 

 Heat cannot pass of itself from one body into another the tem- 

 perature of which is higher — that is to say, without there being 

 at the same time a conversion of work into heat, or vice versa. 



* Bourget, "Theorie mathematique des effets dynamiques de la cha- 

 leur donnee a un gaz permanent/' Annates de Chimie et de Physique, S. 4. 

 vol. lvi. 1859. 



t Marc Saguin, De Vinjiuence des Chemins defer, 1839. 



X Jules Robert Mayer, in Wohler and Liebig's Annalen der Chemie und 

 Pharmacie, vol. xlii. 1842. 



G2 



