154 Prof. E. Rutherford on Uranium Radiation and 



Plates 2*5 cm. apart. 





Plates *5 cm. apart. 



Volts. 



Current R 1 . 



Volts. 1 Current E r 



•5 



1 



2 



4 



8 



16 



37-5 



112 



375 



800 



425 

 825 

 1570 

 2750 

 3750 

 4230 

 4700 

 5250 

 5625 

 5825 



■125 

 •25 

 •5 

 1 

 2 

 4 

 8 

 16 

 100 

 335 



1400 

 2800 

 4300 

 5250 

 5650 

 6200 

 6670 

 6950 

 7400 

 7850 



Under the column of volts the difference of potential 

 between A and B is given. The current is given in terms of 

 the resistance E-x required to keep the electrometer at the 

 earth zero. It will be observed that for the first few readings 

 Ohm's Law is approximately obeyed, and then the current 

 increases more gradually till for large E.M.F/s the rate of 

 increase is very slow. For the plates '5 cm. apart the 

 rate of leak for 335 volts is only 50 per cent, greater than 

 the rate of leak for 1 volt. 



The same general results are obtained if the surface of the 

 uranium is bare or covered with thin metal. The disadvantages 

 of covering the surface with thin tin or aluminium foil are (1) 

 that the intensity of the radiation is considerably decreased ; 

 (2) that the ions diffuse from under the tinfoil through any 

 small holes or any slight openings in the side. The drawback 

 of using the uncovered uranium in the form of fine powder 3 

 is that under large electric forces the fine uranium particles 

 are set in motion between the plates and cause an additional 

 leakage. In practice the rate of leak was measured with 

 potential-differences too small to produce any appreciable 

 action of this kind. 



In order to investigate the current-electromotive-force 

 relations for different gases the same method was used, but 

 the leakage in this case took place between two concentric 

 cylinders. The apparatus is shown in the lower part of 

 fig. 12 : C and D were two concentric cylinders of brass 4*5 

 and 3*75 cm. in diameter, insulated from each other. 



