171 



circle on tlie same axis. It was then found tliat altliough the 

 HI in air appeared to decrease as the temperature of the ra- 

 dium apparatus was raised, yet when the readings were ex- 

 pressed in terms of the uranium scale, the value of Rl was 

 constant. The decline was merely apparent, and due to leak- 

 age through the heated glass insulators. The actual values of 

 l\l were : — 



Five determinations, 20" to 60^ C. : 320, 326, 318, 314, 

 314: mean, 319. 



Five determinations, 60" to 80'^ C. : 296. 314, 311, 334, 

 327; mean, 316. 



The experiments were made at various times, and some 

 of the irregularities are probably due to slight alterations in 

 the amount of RaC present. 



Furthermore, it has already been shown with respect to 

 ionisation in general that pressure and temperature have no 

 effect (Patterson, Proc. Roy. Soc, 69, p. 277, 1901, and "Phil. 

 Mag.," Aug., 1903). I have thought it well, however, to re- 

 consider the point with special reference to the circumstances 

 of this experiment. 



It is convenient at this stage to state that temperature 

 does not seem to have much effect on initial recombination. 

 The latter decreases rapidly as pressure is lowered. This has 

 been shown by Kleeman and myself ("On the Recombination 

 of Ions, etc."). But when the alteration in density occa- 

 sioned by a rise of temperature has been allowed for, there 

 appears to remain only a slight diminution in initial recombi- 

 nation, which can be ascribed to the direct result of the in- 

 crease in temperature. This is shown with some clearness in 

 some experiments which I have made with CO.j. They may 

 be tabulated as follows, the ionisation at an electric force of 

 1,000 volts iDer cm. being taken as 100 : — 



Ionisation Ionisation Ionisation 



A repetition of the experiment gave practically the same 

 result. The press uras and temperatures were so arranged 

 that the density was the same in each experiment. 



I also tried the experiment with ethyl chloride, but the 

 results were not so definite ; that is to say, change^ of tem- 

 perature produced no very obvious effect. 



