156 
COLLECTIONS AND RECOLLECTIONS. 
fluids composing the visible surface are maintained, and the continual 
generation and filling in of the pores, vvithout having recourse to inter¬ 
nal causes. The mode of action here alluded to, is perfectly represented 
to the eye in the disturbed subsidence of a precipitate, as described 
in Art. 330., when the fluid from which it subsides is warm, and lo¬ 
sing heat from its surface. 
The sun’s rays are the ultimate source of almost every motion 
which takes place on the surface of the earth. By its heat are pro¬ 
duced all winds, and those disturbances in the electric equilibrium of 
the atmosphere which give rise to. the phenomena of terrestrial mag- 
nestism. By their vivifying action, vegetables are elaborated from 
inorganic matter, and become, in their turn, the support of animals 
and of man, and the sources of those great deposits of dynamical ef¬ 
ficiency, 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 equilibriun of the 
elements of nature, which by a series of compositions and decomposi¬ 
tions, give rise to new products, and originate a transfer of materials. 
Even the slow degradation of the solid constituents of the suYface, in 
which its chief geological changes consist, and their diffusion among 
the waters of the ocean, are entirely due to the abrasion of the wind 
and rain, and the alternate action of the seasons; and when we con¬ 
sider the immense transfer of matter so produced, the increase of 
pressure over large spaces in the bed of the ocean, and dimunition 
over corresponding portions of the land, we are not at a loss to per¬ 
ceive how the elastic power of subterranean fires, thus repressed on 
the one hand and relieved on the other, may break forth in points 
when the resistance is barely adequate to their retention, and thus 
bring the phenomena of even volcanic activity under the general law 
of solar influence. 
The great mystery, however, is to conceive how so enormous a 
conflagration (if such it be) can he kept up. Every discovery in 
chemical science here leaves us completely at a loss, or rather, seems 
to remove farther the prospect of probable explanation. If conjec¬ 
ture might be hazarded, we should look rather to the known possi¬ 
bility of an indefinite generation of heat by friction, or to its excite¬ 
ment by the electric discharge, than to any actual combustion of pon¬ 
derable fuel, whether solid or gaseous, for the origin of the solar 
radiation .*—Herschell in Lard. Cab. Cyclop. 
* Electricity traversing excessively rarefied air or vapours, gives out light, and 
doubtless, also heat. May not a continual current of electric matter be con- 
