BOOK X. 



THERMOTICS. ATMOLOGY. 



CHAPTER III. 

 THE RELATION OF VAPOUR AND Am. 



Sect. 4. Force of Steam. 



THE experiments on the elastic force of steam made by the French 

 Academy are fitted in an especial manner to decide the question 

 between rival formulae, in consequence of the great amount of force to 

 which they extend ; namely, 60 feet of mercury, or 24 atmospheres : 

 for formulae which give results almost indistinguishable in the lower 

 part of the scale diverge widely at those elevated points. Mr. Waters- 

 ton 1 has reduced both these and other experiments to a rule in the 

 following manner : He takes the zero of gaseous tension, determined 

 by other experimenters (Rudberg, Magnus, and Regnault,) to be 461 

 below the zero of Fahrenheit, or 2Y4 below the zero of the centigrade 

 scale : and temperatures reckoned from this zero he calls " G tempera- 

 tures." The square root of the G temperatures is the element to which 

 the elastic force is referred (for certain theoretical reasons), and it is found 

 that the density of steam is as the sixth power of this element. The 

 agreement of this rule with the special results is strikingly close. A 

 like rule was found by him to apply generally to many other gases in 

 contact with their liquids. 



But M. Regnault has recently investigated the subject in the most 

 iomplete and ample manner, and has obtained results somewhat 

 different. 2 He is led to the conclusion that no formula proceeding by 



1 Phil. Trans. 1852. 



2 Mem. de I'lnstitut, vol. xxi. (1847). M. Regnault's Memoir occupies 761 



sages. 



