34 COSMOS. 



have their origin in analogous kinds of motion (currents). It 

 is reserved for future ages to make great discoveries in ref- 

 erence to these 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.* Even far from its surface, in 

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

 electro-magnetic currents, which exert their exciting influ- 

 ence on the combinations and decompositions of matter on 

 all formative agencies in the mineral kingdom on the dis- 

 turbance 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 ac- 

 cordance with an early hypothesis of Sir "William Herschel,t 

 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, trans- 

 mitted in the regions of space by vibrations of ether, may be 

 accompanied by electro-magnetic currents. 



Direct observations on the periodic changes in the decli- 

 nation, inclination, and intensity of terrestrial magnetism, 

 have, it is true, not yet shown with certainty that these con- 

 ditions are affected by the different positions of the sun or 

 moon, notwithstanding the latter's contiguity to the earth. 

 The magnetic polarity of the earth exhibits no variations 

 that can be referred to the sun, or which perceptibly affect 

 the precession of the equinoxes. t The remarkable rotatory 

 or oscillatory motion of the radiating cone of light of Halley's 

 comet, which Bessel observed from the 12th to the 22d of 

 October, 1835, and endeavored to explain, led this great as- 

 tronomer to the conviction that there existed a polar force, 



Compare the fine passage on me influence of the sun's rays in Sir 

 n Herschel's Outlines of Astronomy, p. 237 : " By the vivifying ac- 

 tion of the sun's rays, vegetables are enabled to draw support from in- 



organic 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 coo 1 , strata. By them the wa- 

 ters of the sea are made to circulate in v*pT through the air, and irri- 

 gate 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." 



t Philos. Transact, for 1795, vol. Ixxxv., p. 318 ; John Herschel, Out- 

 lines of Astr., p. 238; see also Cosmos, vol. i., p. 189. 



t See Bessel, in Schumacher's Astr. Nachr., bd. xiii., 1836, No. 300, 

 B. 201. 



