Sir John Herschel estimates the total Expenditure of Heat by the Sun in
a given time, by supposing a cylinder of ice 45 miles in diameter to be
continually darted into the sun _with the velocity of light_, and that
the water produced by its fusion were continually carried off: the heat
now given off constantly by radiation would then be wholly expended in
its liquefaction, on the one hand, so as to leave no radiant surplus;
while, on the other, the actual temperature at its surface would
undergo no diminution.
The great mystery, however, is to conceive how so enormous a
conflagration (if such it be) can be kept up. Every discovery in
chemical science here leaves us completely at a loss, or rather
seems to remove further the prospect of probable explanation. If
conjecture might be hazarded, we should look rather to the known
possibility of an indefinite generation of heat by friction, or to
its excitement by the electric discharge, than to any combustion of
ponderable fuel, whether solid or gaseous, for the origin of the solar
radiation.--_Outlines._[43]