298 Danysz and, Duane — Electric Charges of a- and ^-Rays. 



would be saturated by very small electric forces. Further 

 special series of experiments have shown that the gas pressure 

 has no effect on the currents provided it is below certain values 

 easily obtainable with the Gaede pump. The use of carbon 

 and liquid air to reduce the pressure below that reached with 

 the pump was found to be quite unnecessary. 



The currents are undoubtedly the results of the superposition 

 of the charges carried by the secondary rays due to the a-rays 



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on those carried by the a- and /3-rays themselves. These 

 secondary rays are produced at the surfaces of the sheets of 

 aluminium, both that attached to the bottom of E and that 

 covering the hole C. Only those between the sheets count, for 

 the others remain within their respective boxes and do not 

 alter the charge received by the box E. If there is no differ- 

 ence of potential between the boxes B and E the secondary 

 rays projected down from the upper sheet more or less balance 

 those projected upward from the lower sheet. One cannot 

 be sure, however, that there is an exact balance, and that the 

 charge measured under these conditions is the charge of the a- 

 and /3-rays themselves, for the a-rays traverse the sheets upward 



