Lowndean Professor of Astronomy and Geometry at Cambridge, England;
formerly Royal Astronomer of Ireland.
There is a story told of a well-intentioned missionary who tried to
induce a Persian fire-worshipper to abandon the creed of his
ancestors. "Is it not," urged the Christian minister, "a sad and
deplorable superstition for an intelligent person like you to worship
an inanimate object like the sun?" "My friend," said the old Persian,
"you come from England; now tell me, have you ever seen the sun?" The
retort was a just one; for the fact is, that those of us whose lot
requires them to live beneath the clouds and in the gloom which so
frequently brood over our Northern latitudes, have but little
conception of the surpassing glory of the great orb of day as it
appears to those who know it in the clear Eastern skies. The Persian
recognizes in the sun not only the great source of light and of
warmth, but even of life itself. Indeed, the advances of modern
science ever tend to bring before us with more and more significance
the surpassing glory with which Milton tells us the sun is crowned. I
shall endeavor to give in this article a brief sketch of what has
recently been learned as to the actual warmth which the sun possesses
and of the prodigality with which it pours forth its radiant
treasures.
I number among my acquaintances an intelligent gardener who is fond of
speculating about things in the heavens as well as about things on the
earth. One day he told me that he felt certain it was quite a mistake
to believe, as most of us do believe, that the sun up there is a hot,
glowing body. "No," he said; "the sun cannot be a source of heat, and
I will prove it. If the sun were a source of heat," said the rural
philosopher, "then the closer you approached the sun the warmer you
would find yourself. But this is not the case, for when you are
climbing up a mountain you are approaching nearer to the sun all the
time; but, as everybody knows, instead of feeling hotter and hotter as
you ascend, you are becoming steadily colder and colder. In fact, when
you reach a certain height, you will find yourself surrounded by
perpetual ice and snow, and you may not improbably be frozen to death
when you have got as near to the sun as you can. Therefore," concluded
my friend, triumphantly, "it is all nonsense to tell me the sun is a
scorching hot fire."
[Illustration: THE SUN: FROM A PHOTOGRAPH TAKEN BY LEWIS M. RUTHERFURD
IN NEW YORK, SEPTEMBER 22, 1870.
Professor C. A. Young, writing to the editor of MCCLURE'S MAGAZINE,
pronounces this "still the best photograph of the entire sun" with
which he is acquainted.]
I thought the best way to explain the little delusion under which the
worthy gardener labored was to refer him to what takes place in his
own domain. I asked him wherein lies the advantage of putting his
tender plants into his greenhouse in November. How does that preserve
them through the winter? How is it that even without artificial heat
the mere shelter of the glass will often protect plants from frost? I
explained to him that the glass acts as a veritable trap for the
sunbeams; it lets them pass in, but it will not let them escape. The
temperature within the greenhouse is consequently raised, and thus the
necessary warmth is maintained. The dwellers on this earth live in
what is equivalent, in this respect, to a greenhouse. There is a
copious atmosphere above our heads, and that atmosphere extends to us
the same protection which the glass does to the plants in the
greenhouse. The air lets the sunbeams through to the earth's surface,
and then keeps their heat down here to make us comfortable. When you
climb to the top of a high mountain you pass through a large part of
the air. This is the reason why you feel warmer on the surface of the
earth than you do on the top of a high mountain. If, however, it were
possible to go very much closer to the sun; if, for example, the earth
were to approach within half its present distance, it is certain that
the heat would be so intense that all life would be immediately
scorched away.
It will be remembered that when Nebuchadnezzar condemned the unhappy
Shadrach, Meshach, and Abednego to be cast into the burning fiery
furnace, he commanded in his fury that the furnace should be heated
seven times hotter than it was wont to be heated. Let us think of the
hottest furnace which the minions of Nebuchadnezzar could ever have
kindled with all the resources of Babylon; let us think indeed of one
of the most perfect of modern furnaces, in which even a substance so
refractory as steel, having first attained a dazzling brilliance, can
be melted so as to run like water; let us imagine the heat-dispensing
power of that glittering liquid to be multiplied sevenfold; let us go
beyond Nebuchadnezzar's frenzied command, and imagine the efficiency
of our furnace to be ten or twelve times as great as that which he
commanded--we shall then obtain a notion of a heat-giving power
corresponding to that which would be found in the wonderful celestial
furnace, the great sun in heaven.
[Illustration: SIR ROBERT BALL. From a photograph by Russel & Sons,
London.]
Ponder also upon the stupendous size of that orb, which glows at every
point of its surface with the astonishing fervor I have indicated. The
earth on which we stand is no doubt a mighty globe, measuring as it
does eight thousand miles in diameter; yet what are its dimensions in
comparison with those of the sun? If the earth be represented by a
grain of mustard seed, then on the same scale the sun should be
represented by a cocoanut. Perhaps, however, a more impressive
conception of the dimensions of the great orb of day may be obtained
in this way. Think of the moon, the queen of the night, which circles
monthly around our heavens, pursuing, as she does, a majestic track,
at a distance of two hundred and forty thousand miles from the earth.
Yet the sun is so vast that if it were a hollow ball, and if the earth
were placed at the centre of that ball, the moon could revolve in the
orbit which it now follows, and still be entirely enclosed within the
sun's interior.
For every acre on the surface of our globe there are more than ten
thousand acres on the surface of the great luminary. Every portion of
this illimitable desert of flame is pouring forth torrents of heat. It
has indeed been estimated that if the heat which is incessantly
flowing through any single square foot of the sun's exterior could be
collected and applied beneath the boilers of an Atlantic liner, it
would suffice to produce steam enough to sustain in continuous
movement those engines of twenty thousand horse-power which enable a
superb ship to break the record between Ireland and America.
The solar heat is shot forth into space in every direction, with a
prodigality which seems well-nigh inexhaustible. No doubt the earth
does intercept a fair supply of sunbeams for conversion to our many
needs; but the share of sun-heat that the dwelling-place of mankind is
able to capture and employ forms only an infinitesimal fraction of
what the sun actually pours forth. It would seem, indeed, very
presumptuous for us to assume that the great sun has come into
existence solely for the benefit of poor humanity. The heat and light
daily lavished by that orb of incomparable splendor would suffice to
warm and illuminate, quite as efficiently as the earth is warmed and
lighted, more than two thousand million globes each as large as the
earth. If it has indeed been the scheme of nature to call into
existence the solar arrangements on their present scale for the
solitary purpose of cherishing this immediate world of ours, then all
we can say is that nature carries on its business in the most
outrageously wasteful manner.
What should we think of the prudence of a man who, having been endowed
with a splendid fortune of not less than twenty million dollars, spent
one cent of that vast sum usefully and dissipated every other cent and
every other dollar of his gigantic wealth in mere aimless
extravagance? This would, however, appear to be the way in which the
sun manages its affairs, if we are to suppose that all the solar heat
is wasted save that minute fraction which is received by the earth.
Out of every twenty million dollars' worth of heat issuing from the
glorious orb of day, we on this earth barely secure the value of one
single cent; and all but that insignificant trifle seems to be utterly
squandered. We may say it certainly is squandered so far as humanity
is concerned. No doubt there are certain other planets besides the
earth, and they will receive quantities of heat to the extent of a few
cents more. It must, however, be said that the stupendous volume of
solar radiation passes off substantially untaxed into space, and what
may actually there become of it science is unable to tell.
And now for the great question as to how the supply of heat is
sustained so as to permit the orb of day to continue in its career of
such unparalleled prodigality. Every child knows that the fire on the
domestic hearth will go out unless the necessary supplies of wood or
coal can be duly provided. The workman knows that the devouring blast
furnace requires to be incessantly stoked with fresh fuel. How, then,
comes it that a furnace so much more stupendous than any terrestrial
furnace can continue to pour forth in perennial abundance its amazing
stores of heat without being nourished by continual supplies of some
kind? Professor Langley, who has done so much to extend our knowledge
of the great orb of heaven, has suggested a method of illustrating the
quantity of fuel which would be required, if indeed it were by
successive additions of fuel that the sun's heat had to be sustained.
Suppose that all the coal seams which underlie America were made to
yield up their stores. Suppose that all the coal fields of England and
Scotland, Australia, China, and elsewhere were compelled to contribute
every combustible particle they contained. Suppose, in fact, that we
extracted from this earth every ton of coal it possesses, in every
island and in every continent. Suppose that this vast store of fuel,
which is adequate to supply the wants of this earth for centuries,
were to be accumulated in one stupendous pile. Suppose that an army of
stokers, arrayed in numbers which we need not now pause to calculate,
were employed to throw this coal into the great solar furnace. How
long, think you, would so gigantic a mass of fuel maintain the sun's
expenditure at its present rate? I am but uttering a deliberate
scientific fact when I say that a conflagration which destroyed every
particle of coal contained in this earth would not generate so much
heat as the sun lavishes abroad to ungrateful space in the tenth part
of every single second. During the few minutes that the reader has
been occupied over these lines, a quantity of heat which is many
thousands of times as great as, the heat which could be produced by
the ignition of all the coal in every coal-pit in the globe has been
dispersed and totally lost to the sun.
But we have still one further conception to introduce before we shall
have fully grasped the significance of the sun's extravagance in the
matter of heat. As the sun shines to-day on this earth, so it shone
yesterday, so it shone a hundred years ago, a thousand years ago; so
it shone in the earliest dawn of history; so it shone during those
still remoter periods when great animals flourished which have now
vanished forever; so it shone during that remarkable period in earth's
history when the great coal forests flourished; so it shone in those
remote ages many millions of years ago when life began to dawn on an
earth which was still young. There is every reason to believe that
throughout these illimitable periods which the imagination strives in
vain to realize, the sun has dispensed its radiant treasures of light
and warmth with just the same prodigality as that which now
characterizes it.
We all know the consequences of wanton extravagance. We know it spells
bankruptcy and ruin. The expenditure of heat by the sun is the most
magnificent extravagance of which human knowledge gives us any
conception. How have the consequences of such awful prodigality been
hitherto averted? How is it that the sun is still able to draw on its
heat reserves from second to second, from century to century, from eon
to eon, ever squandering two thousand million times as much heat as
that which genially warms our temperate regions, as that which draws
forth the exuberant vegetation of the tropics, or which rages in the
Desert of Sahara? This is indeed a great problem.
It was Helmholtz who discovered that the continual maintenance of the
sun's temperature is due to the fact that the sun is neither solid nor
liquid, but is to a great extent gaseous. His theory of the subject
has gained universal acceptance. Those who have taken the trouble to
become acquainted with it are compelled to admit that the doctrine set
forth by this great philosopher embodies a profound truth.
[Illustration: A TYPICAL SUN-SPOT.
By permission of Longmans, Green & Co., from "Old and New Astronomy,"
by Richard A. Proctor.]
Even the great sun cannot escape the application of a certain law
which affects every terrestrial object, and whose province is wide as
the universe itself. Nature has not one law for the rich and another
for the poor. The sun is shedding forth heat, and therefore, affirms
this law, the sun must be shrinking in size. We have learned the rate
at which this contraction proceeds; for among the many triumphs which
mathematicians have accomplished must be reckoned that of having put a
pair of callipers on the sun so as to measure its diameter. We thus
find that the width of the great luminary is ten inches smaller to-day
than it was yesterday. Year in and year out the glorious orb of heaven
is steadily diminishing at the same rate. For hundreds of years, aye,
for hundreds of thousands of years, this incessant shrinking has gone
on at about the same rate as it goes on at present. For hundreds of
years, aye, for hundreds of thousands of years, the shrinking still
will go on. As a sponge exudes moisture by continuous squeezing, so
the sun pours forth heat by continuous shrinking. So long as the sun
remains practically gaseous, so long will the great luminary continue
to shrink, and thus continue its gracious beneficence. Hence it is
that for incalculable ages yet to come the sun will pour forth its
unspeakable benefits; and thence it is that, for a period compared
with which the time of man upon this earth is but a day, summer and
winter, heat and cold, seedtime and harvest, in their due succession,
will never be wanting to this earth.