126 



THE ROYAL SOCIETY OF CANADA 



found in divisions per minute. The results obtained are given in 

 Table I, the initial readings in column 3 of the table. 



TABLE I 



Absorbing 

 Material 



0.0 



0.9 cm. of air 



1 >-j u u u 



air + 1 paper sheet 

 air+2 paper sheets 

 air+3 paper sheets 

 air +4 paper sheets 

 air+5 paper sheets 

 air+6 paper sheets 

 air +22 paper sheets 

 air +30 paper sheets 



Mass in 

 gms/cm^ 



0.00011 

 0.00021 

 0.00893 

 0.0177 

 0. 0265 

 0.0353 

 0. 0-140 

 0, 0528 

 0. 1953 

 0.2655 



Divisions 

 per minute 



25.6 

 17.2 

 16.7 

 11.36 

 9.46 

 8.86 

 7.80 

 7.40 

 7.18 

 7.00 

 6.98 



Intensity of 

 Secondary /3-rays 



Uncorrected Corrected 



18 

 10 

 9 

 4 

 2 

 1 



6 

 2 



7 



36 

 46 

 86 

 80 

 40 

 18 

 00 



14 9 

 8.9 

 8.6 

 4 13 

 2 41 

 1 86 

 80 

 40 

 18 

 00 



The readings in column 3 are for the combined effects of: 

 (1) secondary /3-rays entering the electroscope from below, (2) X-rays 

 and 7-rays v/hich have passed through the absorption sheets. The 

 mass absorption coefficient of the latter in paper being 0.074, the 

 absorbing layers of paper have very little effect on their intensity. 

 Consequently, a standard reading of 7 divisions per m.inute was taken 

 as the intensity due to (2). Subtracting this from the figures in 

 column 3, we get those in column 4. Another correction has to be 

 made because of the /3-rays excited by the 7-rays of radium D, the 

 initial intensity of such /3-rays being about 20 per cent, of the total 

 i.e., one of 3.7 divisions per minute. 



A special experiment similar to that described above showed that 

 the following figures represent the absorption of the /3-rays formed by 

 the 7-rays (see Table II), the initial intensity being taken as 3.7. 



TABLE II 



