256 Mr. J. J. Thomson on the 



which is an equation of exactly the same form as the one we 

 obtained on the first hypothesis ; hence we could not distin- 

 guish between these hypotheses by observing the quantity of 

 water formed when there is equilibrium. 



But if the water is absorbed as soon as it is formed, and 

 a steady stream of oxygen and hydrogen flows into the vessel 

 where combination takes place at such a rate as to keep the 

 pressuro there constant, and if v molecules of hydrogen flow 

 into this vessel per unit time, then we have on the first 

 hypothesis, since v molecules of water must be absorbed in 

 unit time, 



and 



np 



T 2 



't 4 t 2 



t 2 2 



(H) o*> 



We know n and q, for they are the number of molecules of 

 hydrogen and oxygen respectively in the vessel where com- 

 bination takes place, and we may suppose t 2 determined by 

 observations on oxygen alone. 



On the second hypothesis the equations are 





rrr n 



T 4 h 



hence we see that 



"-^yK) « 



This equation is not the same as the previous one ; we may 

 suppose that t ± has been found by experiments on hydrogen 

 alone. So that by making experiments in the way we have 

 described, and measuring the rate at which hydrogen and 

 oxygen must flow into the vessel where the combination takes 

 place so as to keep the pressure there constant, we could de- 

 termine whether equation (19) or (20) agreed best with the 

 results of the experiments, and in this way determine which 

 is the right hypothesis. 



The case we have just considered includes also the theory 



