ing how sunlight is decomposed into its primary colours. What we
call white light is composed of seven different colours. The diagram is
relieved of all detail which would unduly obscure the simple process by
which a ray of light is broken up by a prism into different
wave-lengths. The spectrum rays have been greatly magnified.]

IS THE SUN DYING?

Sec. 3

Now let us return to our consideration of the sun.

To us on the earth the most patent and most astonishing fact about the
sun is its tremendous energy. Heat and light in amazing quantities pour
from it without ceasing.

Where does this energy come from? Enormous jets of red glowing gases can
be seen shooting outwards from the sun, like flames from a fire, for
thousands of miles. Does this argue fire, as we know fire on the earth?
On this point the scientist is sure. The sun is not burning, and
combustion is not the source of its heat. Combustion is a chemical
reaction between atoms. The conditions that make it possible are known
and the results are predictable and measurable. But no chemical reaction
of the nature of combustion as we know it will explain the sun's energy,
nor indeed will any ordinary chemical reaction of any kind. If the sun
were composed of combustible material throughout and the conditions of
combustion as we understand them were always present, the sun would burn
itself out in some thousands of years, with marked changes in its heat
and light production as the process advanced. There is no evidence of
such changes. There is, instead, strong evidence that the sun has been
emitting light and heat in prodigious quantities, not for thousands, but
for millions of years. Every addition to our knowledge that throws light
on the sun's age seems to make for increase rather than decrease of its
years. This makes the wonder of its energy greater.

And we cannot avoid the issue of the source of the energy by saying
merely that the sun is gradually radiating away an energy that
originated in some unknown manner, away back at the beginning of things.
Reliable calculations show that the years required for the mere cooling
of a globe like the sun could not possibly run to millions. In other
words, the sun's energy must be subject to continuous and more or less
steady renewal. However it may have acquired its enormous energy in the
past, it must have some source of energy in the present.

The best explanation that we have to-day of this continuous accreti