Rays of Radioactive Substances. 321 



is directly proportional to the emanating power of the com- 

 pound, and is due to the deviable rays produced by excited 

 radioactivity on the walls of the vessel. 



These results point to the conclusion that a portion, at 

 least, of the deviable rays from thorium is due to the presence 

 of excited radioactivity throughout the mass of the compound 

 itself. If the emanation, which is apparently produced by all 

 thorium compounds, is unable to escape rapidly into the air 

 it produces excited radioactivity throughout the compound. 

 In the deemanated oxide consequently more excited radio- 

 activity is produced than in the ordinary oxide, from which 

 more emanation escapes into the air. Since excited radio- 

 activity gives rise to deviable ravs the effect will be greater 

 for the deemanated than the ordinary oxide. 



§ 5. Deviable Rays from Excited Radiations due to 

 Thorium and Radium.. 



A small proportion of the rays emitted by thorium- and 

 radium-excited radiation is deviable by a magnetic field. As 

 these excited radiations decay with the time it w r as of im- 

 portance to see if the deviable rays decayed at the same rate. 



A lead wire was made the cathode in a cylindrical closed 

 vessel containing the emanation from radium, which had 

 been obtained by bubbling air through a solution of radium 

 chloride. The wire was left exposed for one day in order 

 that the excited radiation should have reached a steady value. 

 The lead wire was then bent into a small spiral and placed 

 between the poles of the electromagnet of fig. 1. 



Observations were taken at regular intervals, both of the 

 current due to the deviable and non- deviable rays. Fig. 2 

 (p. 322) shows the results graphically ; Curve 1. shows the 

 decay with time of the non-deviable rays, Curve II. the decay 

 with time of the deviable rays. For the purpose of comparison 

 the maximum value of each is taken as 100. 



Similar observations were made on the excited radio- 

 activity from thoria. 



An aluminium plate, 3x2 cms., was made the cathode in 

 a closed vessel containing about 200 grs. of thoria and left 

 two days. The following table shows the decay of the two 

 types of rays. The initial value of each is taken as unity 

 for comparison : — 



Xon-de viable Deviable 



ravs. 



i 



•83 

 •33 

 •07 



rime. 



rays. 







1 



3 hrs. 



•77 



19 „ 



•38 



42 „ 



•08 



