BOG Rev. P. J. Kirkby : Chemical Effects of the 



being more than balanced by the higher velocities of 

 impact. 



But to be precise, it follows from our collision-hypothesis 

 that ic, p, Y are connected by the functional relation 



p ~*\p)' 



A simple proof of this is the following, which is practically 

 the same as one given by Professor Townsend in connexion 

 with his theory of the genesis of ions by collision. 



Let us suppose that a mass of hydrogen and oxygen is 

 contained in a gas-tight vessel formed by closing a straight 

 glass tube with two metallic electrodes at right angles to the 

 axis of the tube and fitting the tube exactly. Let one of 

 the electrodes be movable like a piston so that, while the 

 mass of gas remains constant, the distance x between the 

 electrodes can be varied. Let the electrodes be kept at a 

 constant potential-difference, and let an ion cross from one 

 to the other in the field of uniform force Y. Then when x 



Y 



is changed —remains constant, for both Y and p vary inversely 



V 

 as x. But for all values of x the number of collisions made 

 by the ion in crossing the gas is the same, and the circum- 

 stances, including the velocity, of each impact are invariable, 

 because the diminution of force is exactly balanced by increase 

 of free path or vice versa. Hence the whole number of dis- 

 sociated atoms and therefore of molecules of water that result 

 is constant. Therefore the number of molecules of water 

 formed by the passage of the ion through a centimetre is 

 inversely proportional to x. But p is also inversely as m 



w Y ■ 



Therefore — is constant while — is constant. 



Hence 



P P 



p j \p j 



The following table gives the values of w and Y for four 

 pressures at which they can be determined from the curves 

 with greatest precision, although the errors of determination 

 maybe larger than (e.g. double) the errors of observation, which 

 may be taken to be about 5 per cent. In the last two columns 



the values of — , — are given. 



