272 Mr. W. Sutherland on 



moving free electrons, whatever may be the gas used to 

 facilitate its flowing. 



We can use Thomson's and Kaufmann's value of mje, 

 namely, about 10~ 7 when e is measured in electromagnetic 

 units, to calculate the order of magnitude of a the radius of 

 the electron. With the relation m/e = 2/jie/3a and /jl = 1 and 

 e=10~ 21 in the electromagnetic system of units, we then 

 have a = 10~ 14 nearly, while the radii of molecules are of the 

 order 10~ 8 cm., so that the linear dimensions of an electron 

 are about the millionth part of those of molecules. We 

 must therefore concede to the electron great freedom of 

 motion in the interstices between the molecules even of solid 

 bodies. 



A very remarkable fact about the equations of motion of 

 the cathode stream used by Thomson is that, although the 

 velocity attained is about one-third that of light, there is no 

 sign of any necessity to take account of appreciable frictional 

 resistance. The electrons stream through the aether with 

 nearly the velocity of light and yet provoke no noticeable 

 resistance. What wonder, then, that any sethereal resistance 

 to planetary motion has remained beyond our ken ! 



The importance of the quantitative results in these experi- 

 ments has necessitated their being discussed out of their 

 historical and logical order in a train of thought on cathode 

 and allied rays, which order we will now attempt to follow 

 briefly. 



Stoney's interpretation of Faraday's law of Electrolysis to 

 mean that electricity exists in separate natural units, the 

 electrons, as definitely as matter in atoms, is now generally 

 accepted, after Helmholtz's independent advocacy of it in 

 his Faraday lecture. 



Many workers have investigated the general dynamics of 

 electrons, but mostly on the supposition that the electron 

 must be associated with an atom, so that they form in con- 

 junction an ion. But if electric action in matter is to be 

 explained only by the participation of electrons, it naturally 

 follows that we should contemplate the existence of electrons 

 in the sether to enable it to play its part in electrical action. 



And next we have to take account of the hypothesis 

 advanced by Helmholtz in his Faraday lecture (Chem. Soc. 

 Trans, xxxix. 1881) to explain Contact Electromotive Force, 

 namely, that different atoms attract electrons with different 

 amounts of force. This hypothesis may not be generally 

 accepted yet, but we propose to follow out its logical con- 

 sequences. If two things attract one another they must be 

 entities of somewdiat the same sort, and therefore the electron is 



