HISTORY OF THE ATOMIC THEOKY. 39 



gives a long table of the force of aqueous vapour at different 

 temperatures, from 40° to 325°. Between 32° and 312° the 

 numbers are given from experiment ; above and below these 

 limits the numbers are from calculation. These tables were 

 afterwards modified by himself, and others have also reduced 

 them to greater accuracy. He objects to the tables from 

 water and alcohol given by M. Betancourt in 1790, and to 

 that in the Encyclopaedia Britannica, because the authors 

 had assumed the force of that from water, at 32°, to be 

 nothing. This constituted one of the steps which the subject 

 made in its rather retarded progress. 



He gives a series of experiments on the power of vapour 

 from liquids, supporting his conclusions by experiments on 

 ether, alcohol, water of ammonia, solution of muriate of lime, 

 mercury, and sulphuric acid, and says " That the variation of 

 the force of vapour from all liquids is the same for the same 

 variation of temperature, reckoning from vapour of any 

 given force; thus assuming a force equal to 30 inches of 

 mercury as the standard, it being the force of vapour from 

 any liquid boiling in the open air, we find aqueous vapour loses 

 half its force by a diminution of 30° of temperature; so 

 does the vapour of any other liquid lose half its force by 

 diminishing its temperature 30° below that in which it boils, 

 and the like for any other increment or decrement of heat." 

 p. 564. 



When speaking of vapour of water in air, he says " the re- 

 sults of all agree in one general rule or principle, which is this ; 

 let 1 represent the space occupied by any kind of air of a 

 given temperature, and free from moisture ; p = the given 

 pressure upon it in inches of mercury; =/*=: the force of 

 vapour from any liquid in that temperature in vacuo ; then 

 the liquid being admitted to the air, an expansion ensues, 

 and the space occupied by the air becomes immediately and 

 in a short time = 1 + 7^5 or which is the same thing = -^ f /. 

 Thus in water for instance, let p = 30 inches/= 15 inches 



