242 Mr. J. J. Thomson on the 





Now 



n 8-78-5-8 K . ' 



^ = kTo — = ' o approximately ; 



/.~/t=l-32, 



n/ 7 



or the free time is 1*32 times the paired time. 



At the temperature of 900° C, since A = 7*8 at the pressure 

 of one atmosphere, we find that 



t -014 

 tN- p ' 



so that at the pressure of one atmosphere T/tN=*014. In the 

 same way as before we find ?i/N"='125; 



,.l / /t=-112, 



or the free time is only about 1/9 of the paired time. 



The close agreement between the observed results and those 

 calculated by equation (4) seems to show that the dissociation 

 in this case is produced by external agency and not by the 

 collision of the molecules themselves. The radiant heat from 

 the sides of the vessel containing the iodine-vapour would 

 tend to dissociate the vapour, and this may be the external 

 agency required. This consideration suggests the view that 

 the absorption of radiant heat by gases may be due, at least 

 in part, to the dissociation of the gas by the radiant heat. 

 This dissociation would absorb energy, and therefore the 

 radiant heat. This view would account for gases whose mole- 

 cular structures are complex absorbing heat much more 

 powerfully than the elementary gases ; for it is very probable 

 that the radiant heat employed in experiments on the absorp- 

 tion of heat by gases is powerful enough to dissociate bodies 

 of complicated structure, but not powerful enough to disso- 

 ciate the elementary gases. We must, however, leave this 

 subject for the present and return to that of chemical combi- 

 nation. 



"We have seen how the ratio of the free to the paired time 

 can be determined by observations made when things have 

 settled down into a state of equilibrium. We cannot, how- 

 ever, by observations of this kind determine t and r separately. 

 To do this we must, as we can see by referring to the diffe- 



