Mr. Norman Campbell on Delta Rays. 



299 



limits of experimental error. The abnormal value for copper 

 is doubtless due to the fact that the polonium is deposited on 

 copper, and seems to suggest that there is still some un- 

 suspected factor influencing the results. The saturating 

 potential was taken at 120 volts, which gave values indis- 

 tinguishable from those at 80 volts. 



On the other hand, the current from the polonium itself is 

 always greater than that from any other substance. This 

 difference is not that between emergence and incidence 

 radiations, for here the polonium is between the two metal 

 electrode surfaces and both radiations are incidence *. 

 Experiments were tried in which the polonium was covered 

 by a thin leaf of the metal forming the cylinder: the following- 

 are the results : — 



Table VIII. 



Al. 



Cu. 





4-18 



5-09 

 5*64 



90 





530 

 79 



Eatio +/- 



It would appear, then, that there is more delta radiation 

 from the polonium than from any other substance, that is to 

 say, there appear to be some true delta rays emitted from 

 the polonium in the process of radioactivity, and not merely 

 excited by the bombardment of the support by the alpha 

 rays. Whether these rays are due to the bombardment of 

 the polonium itself by the alpha rays which it emits, or 

 whether they represent an entirely distinct form of radiation 

 is probably a question of terminology. 



Summary. 



The following statement represents the main results which 

 appear to have been attained in the investigation. 



(1) There is no evidence that the speed of the delta rays 

 is dependent on the speed of the alpha rays exciting them/ 



(2) There is no evidence of any difference in speed between 

 the emergence and incidence radiations. 



* An experiment in which the polonium dij-k was supported from E 

 and surrounded by a cylinder' connected to the electroscope, showed that 

 the result noted was not simply due to the fact that the dish was 

 connected to the measuring- apparatus. 



