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ROYAL SOCIETY OF CANADA 



V. Absorption Experiments. 



In order to obtain an estimate of the penetrating power of 

 the radiations emitted by the potassium salts quantities of the 

 sulphate, the chloride, and the cyanide were spread in turn in uniform 

 layers on a tray and placed beneath and close to the bottom of the 

 ionising chamber AB, Fig. 1. In these measurements the bottom of 

 the chamber consisted of a finely meshed gauze, which permitted the 

 rays to pass into the chamber with as little absorption as possible. 

 The tray containing the salt was then gradually lowered so as to in- 

 crease the air column traversed by the rays before they entered the 

 chamber and the ionisation currents were measured with the salt at 

 different distances. The values of the currents obtained with three 

 of the salts mentioned are shewn in Table 6. These values have 

 been reduced for purposes of comparison to a common maximum in- 

 tensity and the reduced readings are given in Table VII, curves 

 representing them being shewn in Fig. 6. From these it will be 

 seen, just as Campbell and Wood have pointed out, that the rays 

 emitted by potassium salts possess considerable penetrating power. 

 The saturation currents were not reduced to half value until the 

 columns of air traversed amounted to between 12 and 15 cms., and 

 even with the salts at a distance of 40 cm. from the chamber the ionisa- 

 tion currents were still approximately 15 per cent of their highest 

 values. 



TABLE VI. 



Absorption Experiments. 



