Section III., 1909 [ 81 ] Trans. R. S. C. 



VI. — On the Electric Charges Acquired in High Vacua by Insulated 

 Potassium Salts and Other Kadioactive Substances. 



By PuoF. J. C. McLennan. 



(Read before the Roj-al Society of Canada, May 26, 1909.) 



Since the discov(^-y in 1907, by X. E. Caniplx'll and A. Wood/ that 

 potassium salts possess in a very definite though relatively small degree 

 the property of radioactivity, the radiations from these salts have been 

 examined by a number of investigators including among others Camp- 

 bell,2 McLennan and Kennedy,^ and Levin and Kuer.'* 



Amongst other properties of the rays examined by these investi- 

 gators was their absorption by different thicknesses of various substances. 

 From the results of such measurements the view came to be held that the 

 rays from potassium salts were heterogeneous and consisted of several 

 types varying in penetrating power from the beta rays of uranium 

 downwards. The average intensity of the rays, moreover, was found to 

 be about 1/1000 of that of the radiation from uranium salts. 



In a particular set of experiments which were carried out by Camp- 

 bell the rays were passed between the plates of a large zinc grid and on 

 emergence their intensity was ascertained from the conductivity they 

 imparted to a mass of gas in an ionisation chamber. This grid was so 

 arranged that altjrnate plates were metallically connected, and conse- 

 quently when the two sets of plates were joined to the two terminals of 

 aj battery an electric field was established in the intervals between the 

 plates. Campbell found when a field of 8,000 volts was applied to this 

 condenser that the intensity of the emerging rays was diminished by 

 approximately 14 per cent. This led him to the conclusion that the rays 

 consisted of streams of electrically charged particles, and from addi- 

 tional experiments on the direction of the deviation of the deflected 

 beams he concluded that the charge carried by the rays was a negative 

 one. 



It followed therefore from these experiments that the rays in all 

 probability belonged to the beta type of radiation. 



In some absorption experiments made by' the writer, special care was 

 taken to examine the rays from potassium salts for the presence of a 



iProc. Camb. Phil. See. No. 14-15, 1907. 

 aProc. Camb. Phil. Soc. No. H-211, 1907. 

 8 Phil. Mag., Sept., 1908. 

 *Phys. Zeit. 9 Jahr, No. 8, Seite 248. 



