xxxii President's Address. 



of its surface are frequently and violently disturbed and 

 reversed — these apparent and measurable effects are most 

 probably accompanied by others that cannot yet be traced in 

 their complexity. 



The amount of total sun force acting upon the earth must 

 vary considerably between the sun-spot maximum and 

 minimum ; the area occupied by the sun-spots and their 

 penumbra often reaches to a fiftieth of the sun's disc, and on 

 some occasions they have occupied as much as a thirtieth. 

 It can scarcely be conceived that the modification and, 

 perhaps, obliteration of so much of the sun-force acting 

 towards the earth can occur without some change in the 

 condition of her surface and atmosphere. The further physical 

 science advances, the closer and more numerous seem the 

 relations existing between the sun and terrestrial phenomena, 

 and to my mind it appears quite probable that solar physics 

 will, eventually, be found to be the true key to meteorology. 



