Professor Soddy has given an interesting picture of what might happen
when the sun's light and heat is no longer what it is. The human eye
"has adapted itself through the ages to the peculiarities of the sun's
light, so as to make the most of that wave-length of which there is
most.... Let us indulge for a moment in these gloomy prognostications,
as to the consequences to this earth of the cooling of the sun with the
lapse of ages, which used to be in vogue, but which radio-activity has
so rudely shaken. Picture the fate of the world when the sun has become
a dull red-hot ball, or even when it has cooled so far that it would no
longer emit light to us. That does not all mean that the world would be
in inky darkness, and that the sun would not emit light to the people
then inhabiting this world, if any had survived and could keep
themselves from freezing. To such, if the eye continued to adapt itself
to the changing conditions, our blues and violets would be ultra-violet
and invisible, but our dark heat would be light and hot bodies would be
luminous to them which would be dark to us."
§ 12