stars and suns are perhaps the
hottest of all; but it is not improbable that they may be immeasurably
outnumbered by the cold and dark bodies of the universe, which are to us
invisible, and only manifest their existence in an indirect and casual
manner.

The law of cooling tells us that every body radiates heat, and that the
quantity of heat which it radiates increases when the temperature of the
body increases relatively to the surrounding medium. This law appears to
be universal. It is obeyed on the earth, and it would seem that it must
be equally obeyed by every other body in space. We thus see that each of
the planets and each of the stars is continuously pouring forth in all
directions a never-ceasing stream of heat. This radiation of heat is
productive of very momentous consequences. Let us study them, for
instance, in the case of the sun.

Our great luminary emits an incessant flood of radiant heat in all
directions. A minute fraction of that heat is intercepted by our earth,
and is, directly or indirectly, the source of all life, and of nearly
all movement, on our earth. To pour forth heat as the sun does, it is
necessary that his temperature be enormously high. And there are some
facts which permit us to form an estimate of what that temperature must
actually be.

It is difficult to form any numerical statement of the actual
temperature of the sun. The intensity of that temperature vastly
transcends the greatest artificial heat, and any attempt to clothe such
estimates in figures is necessarily very precarious. But assuming the
greatest artificial temperature to be about 4,000 deg. Fahr., we shall
probably be well within the truth if we state the effective temperature
of the sun to be about 14,000 deg. Fahr. This is the result of a recent
investigation by Messrs. Wilson and Gray, which seems to be entitled to
considerable weight.

The copious outflow of heat from the sun corresponds with its enormous
temperature. We can express the amount of heat in various ways, but it
must be remembered that considerable uncertainty still attaches to such
measurements. The old method of measuring heat by the quantity of ice
melted may be used as an illustration. It is computed that a shell of
ice 43-1/2 feet thick surrounding the whole sun would in one minute be
melted by the sun's heat underneath. A somewhat more elegant
illustration was also given by Sir John Herschel, who showed that if a
cylindrical glacier 45 miles