in diameter were to be continually flowing
into the sun with the velocity of light, the end of that glacier would
be melted as quickly as it advanced. From each square foot in the
surface of the sun emerges a quantity of heat as great as could be
produced by the daily combustion of sixteen tons of coal. This is,
indeed, an amount of heat which, properly transformed into work, would
keep an engine of many hundreds of horse-power running from one year's
end to the other. The heat radiated from a few acres on the sun would be
adequate to drive all the steam engines in the world. When we reflect on
the vast intensity of the radiation from each square foot of the sun's
surface, and when we combine with this the stupendous dimensions of the
sun, imagination fails to realise how vast must be the actual
expenditure of heat.

In presence of the prodigal expenditure of the sun's heat, we are
tempted to ask a question which has the most vital interest for the
earth and its inhabitants. We live from hour to hour by the sun's
splendid generosity; and, therefore, it is important for us to know what
security we possess for the continuance of his favours. When we witness
the terrific disbursement of the sun's heat each hour, we are compelled
to ask whether our great luminary may not be exhausting its resources;
and if so, what are the prospects of the future? This question we can
partly answer. The whole subject is indeed of surpassing interest, and
redolent with the spirit of modern scientific thought.

Our first attempt to examine this question must lie in an appeal to the
facts which are attainable. We want to know whether the sun is showing
any symptoms of decay. Are the days as warm and as bright now as they
were last year, ten years ago, one hundred years ago? We can find no
evidence of any change since the beginning of authentic records. If the
sun's heat had perceptibly changed within the last two thousand years,
we should expect to find corresponding changes in the distribution of
plants and of animals; but no such changes have been detected. There is
no reason to think that the climate of ancient Greece or of ancient Rome
was appreciably different from the climates of the Greece and the Rome
that we know at this day. The vine and the olive grow now where they
grew two thousand years ago.

We must not, however, lay too much stress on this argument; for the
effects of slight changes in the sun's heat may have been neutralise