The Heat of the Sun is dissipated and lost by radiation, and must
be progressively diminished unless its thermal energy be supplied.
According to the measurements of M. Pouillet, the quantity of heat
given out by the sun in a year is equal to that which would be produced
by the combustion of a stratum of coal seventeen miles in thickness;
and if the sun’s capacity for heat be assumed equal to that of water,
and the heat be supposed drawn uniformly from its entire mass, its
temperature would thereby undergo a diminution of 20·4° Fahr. annually.
On the other hand, there is a vast store of force in our system capable
of conversion into heat. If, as is indicated by the small density of
the sun, and by other circumstances, that body has not yet reached the
condition of incompressibility, we have in the future approximation of
its parts a fund of heat, probably quite large enough to supply the
wants of the human family to the end of its sojourn here. It has been
calculated that an amount of condensation which would diminish the
diameter of the sun by only the ten-thousandth part, would suffice to
restore the heat emitted in 2000 years.