40 COSMOS. 



subjects. Light, and radiating heat, which is inseparable 

 from it, constitute a main cause of motion and organic 

 life, both in the non-luminous celestial bodies, and on the 

 surface of our planet. 21 Even far from its surface, in the 

 interior of the earth's crust, penetrating heat calls forth electro- 

 magnetic currents, which exert their exciting influence on 

 the combinations and decompositions of matter, on all for- 

 mative agencies in the mineral kingdom on the disturbance 

 of the equilibrium of the atmosphere, and on the functions 

 of vegetable and animal organisms. If electricity moving in 

 currents develops magnetic forces, and if, in accordance with 

 an early hypothesis of Sir William Herschel, 33 the sun itself 

 is in the condition of " a perpetual northern light," (I should 

 rather say of an electro-magnetic storm), we should seem 

 warranted in concluding that solar light, transmitted in the 

 regions of space by vibrations of ether, may be accompanied 

 by electro-magnetic currents. 



Direct observations on the periodic changes in the declina- 

 tion, inclination, and intensity of terrestrial magnetism, have, 

 it is true, not yet shown with cer^ninty that these conditions 



n Compare the fine passage on the influence of the sun's 

 rays, in Sir John Herschel' s Outlines of Astronomy, p. 237 : 

 " By the vivifying action of the sun's rays, vegetables are 

 enabled to draw support from inorganic matter, and become, 

 in their turn, the support of animals and of man, and the 

 sources of those great deposits of dynamical efficiency which 

 are laid up for human use in our coal strata. By them the 

 waters of the sea are made to circulate in vapour through the 

 air, and irrigate the land, producing springs and rivers. By 

 them are produced all disturbances of the chemical equilibrium 

 of -the elements of nature, which, by a series of compositions 

 and decompositions, give rise to new products, and originate 

 a transfer of materials." 



* Philos. Transact, for 1795, vol. Ixxxv. p. 318; John 

 Herschel, Outlines of Astr., p. 238 ; see also Cosmos, vol. i. 

 p. 183. 



