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34 rosMO?.have tlieir origin in analogous kinds of motion (currents). ],is reserved for future ages to make great discoveries in relerenceto these subjects. Light, and radiating heat, whicliis inseparable from it, constitute a main cause of motion andorganic life, both in the non-luminous celestial bodies and onthe surface of our planet.^ Even far from its surface, inthe interior of the earth's crust, penetrating heat calls forthelectro-magnetic currents, which exert their exciting influenceon the combinations and decompositions of matter— onall formative agencies in the kingdom— mineral on the disturbanceof the equilibrium of the atmosphere— and on thefunctions of vegetable and animal organisms. If electricitymoving in currents develops magnetic forces, and if, in accordancewith an early hypothesis of Sir William Herschel,tthe sun itself is in the condition of " a perpetual northernlight" (I should rather say of an electro-magnetic storm), weshould seem warranted in concluding that solar light, transmittedin the regions of space by vibrations of ether, may beaccompanied by electro-magnetic currents.Direct observations on the periodic changes in the declination,inclination, and intensity of terrestrial magnetism,have, it is true, not yet shown with certainty that these conditionsare affected by the different positions of the sun ormoon, notwithstanding the latter's contiguity to the earth.The magnetic polarity of the earth exhibits no variationsthat can be referred to the sun, or which perceptibly affectthe precession of the equinoxes. | The remarkable rotatoryor oscillatory motion of the radiating cone of light of Halley'scomet, which Bessel observed from the 12th to the 22d ofOctober, 1835, and endeavored to explain, led this great astronomerto the conviction that there existed a 2^olar force,* Comparelli.e fine pnssage on rne influence of the sun's raj^s in SirJolm Herscliei's Outlines of Astronomy, p. 237: " By the vivifying actionof tlie sun's rays, vegetables are enabled to draw su})port from inorganicmatter, and become, in tfjeir tuni, the support of animals andof man, and the sources of those great deposits of dynamical efficiencytehich are laid uj) for human vse in our strata. By them the watersof the sea are made to circulate in vnp t through the air, and ini-coo^,gate the land, producing springs and rivers. By them are producedi all disturbances of the chemical equilibrium of the elements of nature,which, by a series of compositions and decompositions, give rise to ne'ivproducts, and oi'iginatea transfer of materials."t Philos. Transact, for 17.9.5, vol. Ixxxv., p. 318 ;John Herschelj Outflines of Astr., p. 238; see also Cosmos, vol. i., p. 189.t See Bessel, in Schumacher's Asfr. Nackr., bd. xiii., 183G, No. 300B. 201.