The Evolution of the Sciences 



the opposite direction, another current is flowing 

 which carries positive electric charges. Now, 

 since electricity has been known, never have 

 electric charges been seen existing independently 

 of a material support. So the logical inference 

 is that these electric charges emanating from 

 the kathode are borne by grains of matter; the 

 gas in the tube must have separated into two 

 parts, which travel in opposite directions bearing 

 contrary charges. What happens within the gas 

 seems analogous to what occurs in the electrolysis 

 of acidulated water or of soda lye, and this 

 analogy is one of our chief reasons for looking 

 on these phenomena in the way we have just 

 explained. This hypothesis is capable of con- 

 firmation, and that is its chief merit. We can 

 determine the speed and the mass of the material 

 elements which travel in this manner inside the 

 Rontgen tube. 



In order to realise this let us examine the 

 corresponding problem of ballistics. Let us 

 consider a ball leaving a cannon at a given 

 angle to the horizon ; its trajectory is a curve, a 

 parabola, which we can determine, and the know- 

 ledge of this trajectory enables us to find the 



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