17 



ON PEOFESSOES AYETON AND PEEEY'S NEW THEOEY OF 

 THE EAETH'S MAGNETISM, WITH A NOTE ON A NEW 

 THEOEY OF THE AUEOEA l 



[Philosophical Magazine, [5], VIII, 102-106, 1879. Proceedings of the Physical Society, 



III, 93-98, 1879] 



Some years ago, while in Berlin, I proved by direct experiment that 

 electric convection produced magnetic action; and I then suggested to 

 Professor Helmholtz that a theory of the earth's magnetism might be 

 based upon the experiment. But upon calculating the potential of 

 the earth required to produce the effect, I found that it was entirely 

 too great to exist without producing violent perturbations in the planet- 

 ary movements, and other violent actions. 



I have lately read Professors Ayrton and Perry's publication of the 

 same theory; and as they seem to have arrived at a result for the 

 potential much less than I did, I have thought it worth while to publish 

 my reasons for the rejection of the theory. 



The first objection to the theory that struck me was, that not only 

 the relative motion but also the absolute motion through space of the 

 earth around the sun might also produce action. And to this end I 

 instituted an experiment as soon as I came home from Berlin. 



I made a condenser of two parallel plates with a magnetic needle 

 enclosed in a minute metal box between them; for I reasoned that, when 

 the plates were charged and were moved forward by the motion of the 

 earth around the sun, they would then act in opposite directions on 

 the enclosed needle, and so cause a deflection when the electrification 

 of the condenser was reversed. On trying the experiment in the most 

 careful manner, there was not the slightest trace of action after all 

 sources of error had been eliminated. 



But the experiment did not satisfy me, as I saw there was some 

 electricity on the metal case surrounding the needle. And so I attacked 

 the problem analytically, and arrived at the curious result that if an 

 electrified system moves forward without rotation through space, the 



1 Read before the Physical Society, June 29th. 



