182 



Prof. E. Rutherford on Radioactivity 



The following measurements were made for each experiment 

 at different voltages : — 



(1) The current between A and B was measured with the 

 thorium oxide in the cylinder. 



(2) After the thorium oxide had been removed and the air 

 blown out, the current between A and B was again 

 determined. 



(3) The cylinder B was then removed and a non-active one 



of the same dimensions substituted and the current 

 again observed. 



The electrometer was brought to the same sensitiveness 

 every day by means of a Thomson Replenisher. For rapid 

 rates of discharge, a condenser of '001 microfarad capacity 

 was placed in the electrometer circuit. 



The current (3) includes the small leak (if any) over the 

 insulators plus the current due to the radioactivity produced 

 in the end paraffin stoppers. The current (2) was due to the 

 radio-active cylinder B, together with the current (3). The 

 current (1) was due to the "emanation" from thorium oxide 

 plus (2) and (3). 



From these three observations it was therefore possible to 

 determine : — 



(a) The rate of discharge due to the thorium alone ; 



(6) The rate of discharge due to radio-active cylinder B 

 alone ; 



(c) The rate of discharge due to radioactivity on the sides 

 and ends of vessel. 



In the following table the results are given for different 

 voltages between cylinders. 



Results are in divisions per second of electrometer-scale. 



Voltage. 



Emanation. 



Eadioactivity. 

 on cylinder B. 



Radioactivity 



on sides and 



ends. 



Total 

 Radioactivity. 



: 



5 



10 



20 



310 



5-3 

 122 

 25-3 

 30-0 

 32-2 



1-32 

 402 

 4-53 

 669 

 7-40 

 9-91 



5-58 

 3-06 

 1-97 

 1-51 

 ■59 

 •75 



6-90 

 7-08 

 6-50 

 8-20 

 7-99 

 1066 



Fig. 10 shows the results graphically. Curve A shows the 

 variation of the current due to the " emanation " with voltage ; 



