PRESIDENTIAL ADDRESSES. 513 



solid rotating bodies such as the earth, or 

 Mars, or Venus, or of hot fluid rotating bodies 

 such as the sun, in straining the circumambient 

 ether, we cannot say that the sun might not be 

 1000, or 10,000, or 100,000 times as intense a 

 magnet as the earth. It is, therefore, a perfectly 

 proper object for investigation to find whether 

 there is, or is not, any disturbance of terrestrial 

 magnetism, such as might be produced by a 

 constant magnet in the sun's place with its mag- 

 netic axis coincident with the sun's axis of rota- 

 tion. Neglecting for the present the seven degrees 

 of obliquity of the sun's equator, and supposing 

 the axis to be exactly perpendicular to the ecliptic, 

 we have an exceedingly simple case of magnetic 

 action to be considered : a magnetic force perpen- 

 dicular to the ecliptic at every part of the earth's 

 orbit and varying inversely as the cube of the 

 earth's distance from the sun. The components of 

 this force parallel and perpendicular to the earth's 

 axis are, respectively, 0*92 and 0*4 of the whole ; 

 of which the former could only be perceived in 

 virtue of the varying distance of the earth from the 

 VOL. II. L L 



