PORTION OF THE COSMOS. THE SUN. 267 



I. 



THE SUN AS A CENTRAL BODY 



" THE luminary of the "World (lucerna Mundi), enthroned 

 in the midst," as Copernicus ( 462 ) terms the solar orb, ac- 

 cording to Theon of Smyrna ( 463 ) the " all animating, pul- 

 sating heart of the Universe/' is to our planet the great 

 source of light and radiant heat, and the exciter not only of 

 many terrestrial electro-magnetic processes, but also of the 

 greater part of the processes of organic vital activity, and more 

 especially of those of vegetable life. The Sun, if we desire 

 to indicate its influences and effects with the greatest gene- 

 rality, may be said to produce changes on the surface of the 

 Earth partly by attraction of mass, as in the ebb and flow 

 of the ocean (if we abstract from the whole effect the portion 

 due to lunar attraction) ; partly by light- and heat-exciting 

 undulations, (transverse vibrations of the ether), operating 

 both directly, and also by the fertilising intermixture of the 

 aerial and aqueous envelopes of the planet, effected through 

 the medium of the evaporation of the liquid element from 

 seas, lakes, and rivers. To the solar agency are also due 

 those atmospheric and oceanic currents occasioned by dif- 



