Theory of Heat and Vapours. 47 



and Vapours*. But in the case of atmospheric air, we like- 

 wise have this well-known equation, 



and it will easily be seen that this latter equation is inconsist- 

 ent with the former one ; for from it we obtain — =s-^^ '-* 



P P 



and this value being substituted in the other equation, we get 



which would prove that the pressure is determined when the 

 temperature is given, a property that certainly is not verified 

 in the atmosphere. It is most evident, that, in atmospheric 

 air, there can be, no general relation between 9, p,p, except 

 the law of Mariotte. 



As the fundamental equation of the Theory of Vapours 

 is inadmissible in the case of atmospheric air, we might at 

 once reject all the deductions from it : but it may be worth 

 while to add a few words in order to throw some light on the 

 calculations which follow. Let 6', p', p', and 6", p", p" be 



other values of Q, p,p; and put /3 = 5^, E = ^-^ ; then 



we get from the last equation, 



5^ = (l+«9).(/-E) 



9^=il + uQ>).{p'l'-E) 

 C-A 



kB 



= (l+«fl") .{p"^ -E): 



and hence 



i>'^ = ^x(/-E) + E 



equations which cannot obtain generally in the atmosphere; 

 because, as has been said, the three equations from which 

 they are derived are not properties of atmospheric air. But 

 if we set aside the theoretical views of Sir J. W. Lubbock, 

 and understand each of the two equations as merely express- 

 ing a relation between the quantities it contains, the two con- 

 stants, (3 and E, will be determined when 6, p, fl', p', 6", p" are 

 found by means of three separate observations. Sir J. W, 



* Theor,, p. 2. 



