PRESIDENTIAL ADDRESSES, 509 



simultaneous magnetic disturbances found by 

 observations at magnetic observatories in different 

 parts of the world ; the award of a Royal medal 

 two years ago to Hertz, for his splendid experi- 

 mental work on electro-magnetic waves and vibra- 

 tions ; and Professor Schuster's communication l 

 to the Royal Society, of June, 1889, on the 

 " Diurnal Variations of Terrestrial Magnetism " ; 

 justify me in saying a few words on the present 

 occasion regarding terrestrial magnetic storms, and 

 the hypothesis that they are due to magnetic waves 

 emanating from the sun. 



Guided by Maxwell's "electro-magnetic theory 

 of light," and the undulatory theory of propagation 

 of magnetic force which it includes, we might hope 

 to perfectly overcome a fifty years' outstanding 

 difficulty in the way of believing the sun to be the 

 direct cause of magnetic storms in the earth, 

 though hitherto every effort in this direction has 

 been disappointing. This difficulty is clearly 

 stated by Professor W. G. Adams, in the following 

 sentences, which 1 quote from his Report to the 



1 Roy. Soc. Proc., vol. 180, 1892, p. 467. 



