29 



The results of one experiment are shown in the following 

 table : — 



2607 *106 -504 517 



The mean of the figures in the last column is '00477. 



In another experiment the thorium was precipitated twice 

 at intervals of two days, and then five times at intervals of 

 twelve hours. The results were as follows : — 



Al. foil X W' ^' A range x 10' 



In this case the mean of the figures in the last column is 

 •00475. As in tlie case of radium, this result is probably a 

 little too high, as it is impossible to get rid of all the radio- 

 active products of thorium, and all these, have ranges higher 

 than thorium itself. For Rutherford has shown that the a 

 particle of the induced activity of thorium has the same pene- 

 trating power as the a particle of the induced activity of 

 radium, and some rough experiments which I have made with 

 Th.X. go to show that, as in the case of Ra, the second and 

 third active products have ranges intermediate between the 

 first and fourth. "^It may also be calculated from an experi- 

 ment of Rutherford's ("Radio-activity," 2nd Ed., p. 263 ^ 

 that the range of the emanation a particle is about 6 cm. ; 

 but it is uncertain how much should be allowed for the stop- 

 ping power of the mica sheet which he used. 



* Note.— An experiment by Schmidt (Phys. Zeit. No. 25, p. 897) has 

 shown that RaA has two-thirds of the penetrating power of RaC. Hence 

 its range must be the longer of the two intermediate ranges, determined 

 by Kleeman and myself, viz., 4-83 ; and the range of the emanation must 

 be 4 "23. Thus in the radio-active sequence each explosion is more violent 

 than the last. 



