338 Prof. W. H. Bragg on the Ionization of 



and temperature. As regards pressure, some results were 

 quoted in a paper " On the Recombination of Ions in Air and 

 other Gases " *, which showed this to be correct in the cases 

 o£ air and ethyl chloride; and further evidence will be found 

 in the results given at the end of this paper. For, without 

 having made any exhaustive comparison of the values of RI 

 at different pressures in each gas, I have often used various 

 pressures in the determination of the specific ionization of a 

 gas; and the general agreement between the results obtained 

 is good evidence that pressure is without effect. 



In the same way, since many determinations in the case 

 of the same gas have been made at different temperatures, the 

 close agreement shows also that temperature has no influence 

 on the ionization. More direct confirmation can be obtained 

 from the following results. During a number of the deter- 

 minations of RI, the ionization-chamber was connected in 

 parallel with a second chamber containing a uranium layer. 

 The ionization currents acted against each other. Thus the 

 values of the currents in the radium apparatus could be 

 determined by balancing against the uranium : the latter was 

 always at the temperature of the room, and therefore formed 

 a fixed standard. The extent of the surface of the uranium 

 could be varied by means of a semaphore, having a graduated 

 circle on the same axis. It was then found that although 

 the RI in air appeared to decrease as the temperature of the 

 radium apparatus was raised, yet when the readings were 

 expressed in terms of the uranium scale, the value of RI was 

 constant. The decline was merely apparent, and due to leakage 

 through the heated glass insulators. The actual values of RI 

 were : — 



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

 314 ; mean, 320. 



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 the RaC present. 



Furthermore, it has already been shown with respect to 

 ionization in general that pressure and temperature have no 

 effect (Patterson, Proc. Roy. Soc. lxix. p. 277, 1901, and 

 Phil. Mag. Aug. 1903). I have thought it well, however, to 

 reconsider 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. 



* Trans. Roy. Soc. S. A. 1905, p. 187 ; Phil, Mag. April, 1900, p. 46G. 



