786 



Dr. Norman Campbell on Delta Rays 



part of the curves have been fully discussed. It was found 

 that the curves for positive and negative P.D.'s were exactly 

 the same when Rontgen rays were used, but not when a rays 

 were used. It was thought that the divergence might be 



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attributed to this cause, but it was found that if the curves 

 for a rays were made yet more asymmetrical by using as a 

 source of those rays the active deposit of thorium on the 

 surface of one of the electrodes in place of the polonium 

 behind the window, no change in the form of the curve 

 obtained by adding positive and negative values was obtained. 

 Nevertheless I am inclined to attribute the divergence to 

 some difference in the distribution of the § rays, and have 

 no hesitation in concluding that the S rays excited by ft rays 

 are precisely similar to those excited by a rays. 1 he properties 

 of the § rays are a function neither of the properties of the 

 ionizing rays nor of the material which they ionize ; they are a 

 function of the properties of some mechanism which is concerned 

 in all ionization. This conclusion appears to me of the highest 

 importance. 



6. Perhaps it is well to remark that these experiments 



