TERRESTRIAL MAGNETISM. 87 



axes of all the planets being directed towards the same 

 quarter. Kepler said expressly, " that the sun may be a 

 magnetic body, and that the force which moves the planets 

 may therefore reside in the sun." ( 77 ) Mass-attraction 

 and gravitation appear here under the symbol of magnetic 

 attraction. Horrebow, ( 78 ) who did not confound gravi- 

 tation with magnetism, was the first who termed the solar 

 light "a perpetual Aurora in the sun's atmosphere, pro- 

 duced by magnetic forces." In more modern times (and 

 the difference is important), the views which have been 

 formed respecting the modus operandi of the sun's action 

 have diverged into two distinct classes. 



It has been considered either that the sun, without being 

 itself magnetic, acts on the magnetism of the earth solely 

 through the medium of its effects in causing variations of 

 temperature (this has been the view entertained by Canton, 

 Ampere, Christie, Lloyd, and Airy), or, as supposed by 

 Coulomb, that the sun being enveloped in a magnetic atmo- 

 sphere^ 9 ) influences the magnetism of the earth by direct 

 action. Earaday's striking discovery of the paramagnetic 

 property of oxygen would indeed remove one great difficulty 

 opposing the first-named view, i. e. the difficulty of supposing 

 with Canton that the sea and the solid crust of the earth 

 have their temperature instantaneously and considerably raised 

 by the passage of the sun over the meridian of the place ; 

 but on the other hand, Colonel Sabine's very extensive 

 combination and sagacious discussion of all the facts of 

 observation have led to the result, that the periodical varia- 

 tions in the earth's magnetic activity do not correspond to, 

 and therefore cannot be assumed to be caused by, the peri- 

 odic variations of temperature which take place within the 



