Mr. J. J. E. Durack on Lenard Rayt 



4.1 



The five values of a p taken from these two series have been 

 plotted in curve IV. It will be seen that four of them lie 



Curve IV. 



15 

 10 













© 



























> 





( 



) s* 









5 

















^s® 















j 



i t 



D t 



5 20 25 



Pressure, mm. 



on a straight line ; this line does not pass through the 

 origin. This may be due to an error in setting the zero of 

 the McLeod gauge or in measuring the ratio of volumes. 



These figures justified one in believing the correctness of 

 former results obtained for a p Jp ; they are larger than those 

 obtained in the former series, probably because larger 

 e.m.f.'s were applied to the gas. 



To avoid the trouble of taking current-E.M.F. curves in 

 all cases and yet be sure the gas was saturated, an E.M.F. 

 was applied to the gas which was a little less than sufficient 

 to give a free fall of 1 volt between collisions of the ions 

 with molecules of air as these ions move towards the plate. 

 This 1 volt free fall has been shown by Prof. Townsend * to 

 give the ions just sufficient velocity to produce others by 

 collisions. This was the plan adopted in working with the 

 galvanometer, and I think it is probable some additional 

 ionization due to the Townsend effect has come in to make 

 a p too large. 



This conclusion that we have come to, viz., that very fast 

 moving ions are less efficient ionizers than slower ones, is in 

 agreement with the discovery of Becquerel, viz., that of all 

 the deflectable Becquerel rays the slower ones are most 

 easily absorbed. But it has been shown by several observers 

 that ionization is proportional to absorption : hence we would 

 expect the slow Becquerel rays to be more efficient ionizers 

 than the fast ones. 



As an explanation of this the following theory was proposed 



* Townsend. loc. cit. 



