THE ETHER OF SPACE 299 



of detecting the spin as is furnished by vision for detect- 

 ing some kinds of vibration. It is supposed to exist when- 

 ever we put a charge into the neighborhood of a magnetic 

 pole. Round the line joining the two, the ether is spinning 

 like a top. I do not say it is spinning fast : that is a ques- 

 tion of its density; it is, in fact, spinning with excessive 

 slowness, but it is spinning with a definite moment of 

 momentum. J. J. Thomson's theory makes its moment of 

 momentum exactly equal to e m, the product of charge 

 and pole; the charge being measured electrostatically and 

 the pole magnetically. 



How can this be shown experimentally? Suppose we 

 had a spinning top enclosed in a case, so that the spin was 

 unrecognizable by ordinary means, it could be detected by 

 its gyrostatic behavior to force. If allowed to "precess" 

 it will respond by moving perpendicularly to a deflecting 

 force. So it is with the charge and the magnetic pole. Try 

 to move either suddenly, and it immediately sets off at 

 right angles to the force. A moving charge is a current, 

 and the pole and the current try to revolve round one 

 another a true gyrostatic action due to the otherwise un- 

 recognizable ethereal spin. The fact of such magnetic rota- 

 tion was discovered by Faraday. 



I know that it is usually worked out in another way, in 

 terms of lines of force and the rest of the circuit; but I 

 am thinking of a current as a stream of projected charges ; 

 and no one way of regarding such a matter is likely to 

 exhaust the truth, or to exclude other modes which are 

 equally valid. Anyhow, in whatever way it is regarded, 

 it is an example of the three rectangular vectors. 



The three vectors at right angles to each other, which 

 may be labelled Current, Magnetism and Motion, respec- 

 tively, or more generally E., H. and V., represent the 

 quite fundamental relation between ether and matter, and 

 constitute the link between Electricity, Magnetism and 

 Mechanics. Where any two of these are present, the third 

 is a necessary consequence. This principle is the basis of 



