150 Prof. E. Rutherford on Uranium Radiation and 



the other to the negative pole of a battery. The middle 

 point of the battery was placed to earth. The water-dropper 

 was connected with the electrometer. The potential at a point 

 was first determined without any uranium near. One plate 

 was then removed, and an exactly similar plate, covered with 

 the uranium compound, substituted. The potential of the 

 point was then observed again. In this way the potential at 

 any point with and without the uranium could be determined. 

 The curve shown in fig. 11 is an example of the potential 

 gradient observed between two parallel plates 6' 6 cm. apart. 

 The dotted line represents the potential gradient when the 

 uranium is removed. The ordinates represent volts and the 

 abscissae distances from the plate covered with the uranium 

 compound. 



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It will be observed that the potential gradient is diminished 

 near the uranium and increased near the other plate. The 

 point of zero potential is displaced away from the uranium. 



From curves showing the potential gradient between two 

 plates, the distribution of free electrification between the plates 

 can be deduced. By Taking the first differential of the curve 



we obtain -j- , the electric force at anv point, and by taking 



dx * . d 2 v 



the second differential of the curve we obtain -j— 2 , which is 



