Light is ascertained to be as veritable a substance as
water. The sun is recognized to be dark, cool, and habitable. Messages
go through the air from kite to kite ten miles apart without visible
agency. Telephonic sounds leap from wire to wire through quite ten feet
of space.

_Present theories of Supply of Sun-heat._

The present theories of the production and dissemination of sun-heat,
are simply accepted for want of better, and not because they account
satisfactorily for the phenomena.

The first and most prominent is the combustion theory, which, though
bearing the seal of ages, is obnoxious both to common and philosophic
reasoning. This theory presupposes a consumption of material beyond all
conception, and the supply of which has been no small tax upon the
scientific imagination. The source of this supply has been claimed to be
the subsidence of useless worlds, and of asteroids, and meteors,
showered down upon its surface. Estimates have been carefully made, and
we are gravely informed of the probable amount of combustive material
required to supply the sun's demands for given periods. It is said that
the coal-fields of Pennsylvania, which would supply the world's
consumption for centuries, would keep the sun's rate of emission for
considerably less than 1/1,000 part of a second. POUILLET estimated the
quantity of heat emitted by the sun per hour to be equal to the supply
of a layer of anthracite coal ten feet thick, spread over the whole
surface of the sun.

The theory advocated by HELMHOLTZ, and by many other scientists, of "the
gradual contraction of the solar orb," and that of SECCHI, "the
dissociation of compound bodies in the sun's substance," are attempts
after a more consistent philosophy.

The foregoing theories pre-suppose the sun to be a glowing fiery mass,
from which, in all directions, issue radiations of heat and light into
space. Of this enormous quantity of radiated heat, the earth is supposed
to receive but 1/2,000,000,000 part.

MEYER observes: "_A general law of nature which knows no exception_ is
the following: _In order to obtain heat, something must be expended._"

This combustion theory therefore calls for an enormous expenditure of
material for generating heat and light, together with a still further
expenditure of force for projecting these into all space, at all
distances. All these theories are therefore inconsistent with the
immutable law of the Conservation of F