128 THOMSON ON CARNOT'S 



affected by its all-pervading influence. An evolu- 

 tion and subsequent absorption of heat generally 

 give rise to a variety of effects ; among which may 

 be enumerated, chemical combinations or decom- 

 positions ; the fusion of solid substances ; the 

 vaporization of solids or liquids ; alterations in the 

 dimensions of bodies, or in the statical pressure 

 by which their dimensions may be modified ; me- 

 chanical resistance overcome ; electrical currents 

 generated. In many of the actual phenomena of 

 nature several or all of these effects are produced 

 together ; and their complication will, if we 

 attempt to trace the agency of heat in producing 

 any individual effect, give rise to much perplex- 

 ity. It will, therefore, be desirable, in laying the 

 foundation of a physical theory of a-ny of the 

 effects of heat, to discover or to imagine phe- 

 nomena free from all such complication, and de- 

 pending on a definite thermal agency ; in which 

 the relation between the cause and effect, traced 



been recently published (under the title " Relation des 

 Experiences," etc.) in the Memoires de I'Institut, of which 

 it constitutes the twenty-first volume (1847). The second 

 part of these researches has not yet been published. [Note 

 of Nov. 5, 1881. The continuation of these researches has 

 now been published ; thus we have for the whole series, 

 vol. i. in 1847 ; vol. ii. in 1862 ; and vol. iii. in 1870.] 



