40 FORESHADOWING OF THE ELECTRON [CH. iv. 



prodigious speed, but it is desirable to make a 

 measurement of that speed. 



The force of propulsion exerted on them indicates 

 that they are highly charged ; and their penetrating 

 power suggests that they are excessively small, so 

 that to them ordinary solids, such as metal sheets, 

 appear porous ; but an experimental method is 

 necessary to determine what may be called their 

 electrochemical equivalent, -that is to say the ratio 

 of their mass or inertia to their electric charge, 

 even if it be not possible to determine the mass 

 and the charge separately. 



In electrolysis the electrochemical equivalent, 

 or the ratio m/e, depends on the nature of the 

 substance; and for hydrogen is of the order 10~ 4 

 in electromagnetic units, as stated in Chapter III. 

 It is a matter of great importance to determine 

 the value of the same ratio for the cathode rays, 

 and to ascertain whether it varies with the substance 

 contained in the vacuum tube, or whether it is the 

 same for all substances being characteristic of 

 a single variety of the flying particle and of nothing 

 else. 



