30 



The general conclusion is, therefore, that uranium, 

 thorium, and radium eject a particles of nearly, if not ex- 

 actly, the same speed. Considering the many parallelisms 

 already known to exist between the processes of disintegration 

 of these substances and their products, this new fact is cer- 

 tainly suggestive. It would be very interesting to know the 

 ranges of Th.X. and Th. emanation.* 



Relative Activities of Uranium and Thorium. 



An expression is found in Part I. of this paper for the 

 total ionisation over an uncovered deep layer of active ma- 

 terial. By its aid we may find the relative numbers of 

 a particles emitted by uranium and thorium when the ionisa- 

 tion currents due to known areas of the layers have been 

 measured. 



Since the ranges are so nearly alike, it is sufficient to use 

 the simpler formula: — 



Nl'n, 



If, now, the suffixes U and T refer to uranium and 

 thorium, we have 



/ TV 7?2„ 



/t Nr R'iSu 



and therefore 



Each time that a thorium experiment was completed a compari- 

 son was made of the currents L^ and 7^. In the first case — 

 was found to be •234 ; in the second -234. 



— -- I as may be seen from the results given above can 

 456\^- 



be taken as equal to I ) =-916. 



^ U76/ 



* Experiments just completed go to show that the particle from Th.B. 

 is rather more penetrating than that from RaC ; and that the particle from 

 Th Em. has a range of about tln^ee fourths of that from Tli.B. It is 

 already known that the range of the particle from RaA is -68 of that from 

 RaC. (April 4, 1906.) 



