PRESIDENTIAL ADDRESS, S.T.E., 1874. 



accordance with any knowledge we have of thermo- 

 electricity, how there could so be sustained currents 

 round the earth. And if there were currents 

 round the earth, regulated by some cause so as to 

 give them a definite direction at one time, we are 

 as far as ever from explaining how the channel 

 of these currents could experience that great re- 

 volutionary variation which we know it does 

 experience. Thus we have merely a mystery. It 

 would be rash to suggest even an explanation. I 

 may say that one explanation has been suggested. 

 It was suggested by the great astronomer, Halley, 

 that there is a nucleus in the interior of the 

 earth, and that the mystery is explained simply 

 by a magnet not rigidly connected with the upper 

 crust of the earth, but revolving round an axis 

 differing from the axis of rotation of the outer 

 crust, and exhibiting a gradual precessional motion 

 independent of the precessional motion of the 

 outer rigid crust. I merely say that has been 

 suggested. I do not ask you to judge of the 

 probability : I would not ask myself to judge of 

 the probability of it. 



