LOWNDEAN PROFESSOR OF ASTRONOMY AND GEOMETRY AT CAMBRIDGE, ENGLAND;
FORMERLY ROYAL ASTRONOMER OF IRELAND.
The light of the great orb of day emanates solely from a closely
fitting robe of surpassing brightness. The great bulk of the sun which
lies within that brilliant mantle is comparatively obscure, and might
at first seem to play but an unimportant part so far as the dispensing
of light and heat is concerned. It may indeed be likened to the
coal-cellar from whence are drawn the supplies that produce the warmth
and brightness of the domestic hearth; while the brilliant robe where
the sun develops its heat corresponds to the grate in which the coal
is consumed. With regard to the thickness of the robe, we might liken
this brilliant exterior to the rind of an orange, while the gloomy
interior regions would correspond to the edible portion of the fruit.
Generally speaking, the rind of the orange is rather too coarse for
the purpose of this illustration. It might be nearer the truth to
affirm that the luminous part of the sun may be compared to the
delicate filmy skin of the peach. There can be no doubt that if this
glorious veil were unhappily stripped from the sun, the great luminary
would forthwith lose its powers of shedding forth light and heat. The
spots which we see so frequently to fleck the dazzling surface, are
merely rents in the brilliant mantle through which we are permitted to
obtain glimpses of the comparatively non-luminous interior.
As the ability of the sun to warm and light this earth arises from the
peculiar properties of the thin glowing shell which surrounds it, a
problem of the greatest interest is presented in an inquiry as to the
material composition of this particular layer of solar substance.
We want, in fact, to ascertain what that special stuff can be which
enables the sun to be so useful to us dwellers on the earth. This
great problem has been solved, and the result is extremely interesting
and instructive; it has been discovered that the material which
confers on the sun its beneficent power is also a material which
is found in the greatest abundance on the earth, where it fulfils
purposes of the very highest importance. Let us see, in the first
place, what is the most patent fact with regard to the structure
of this solar mantle possessed of a glory so indescribable. It is
perfectly plain that it is not composed of any continuous solid
material. It has a granular character which is sometimes perceptible
when viewed through a powerful telescope, but which can be seen more
frequently and studied more satisfactorily on a photographic plate.
These granules have an obvious resemblance to clouds; and clouds,
indeed, we may call them. There is, however, a very wide difference
between the solar clouds and those clouds which float in our own
atmosphere. The clouds which we know so well are, of course, merely
vast collections of globules of water suspended in the air. No doubt
the mighty solar clouds do also consist of incalculable myriads
of globules of some particular substance floating in the solar
atmosphere. The material of which these solar clouds are composed
is, however, I need hardly say, not water, nor is it anything in
the remotest degree resembling water. Some years ago any attempt to
ascertain the particular substance out of which the solar clouds were
formed would at once have been regarded as futile; inasmuch as such a
problem would then have been thought to lie outside the possibilities
of human knowledge. The advance of discovery has, however, shed a
flood of light on the subject, and has revealed the nature of that
material to whose presence we are indebted for the solar beneficence.
The detection of the particular element to which all living creatures
are so much indebted is due to that distinguished physicist, Dr. G.
Johnstone Stoney.
In the whole range of science, one of the most remarkable discoveries
ever made is that which has taught us that the elementary bodies of
which the sun and the stars are constructed are essentially the same
as those of which the earth has been built. This discovery was indeed
as unexpected as it is interesting. Could we ever have anticipated
that a body ninety-three millions of miles away, as the sun is, or a
hundred million of millions of miles distant, as a star may be, should
actually prove to have been formed from the same materials as those
which compose this earth of ours and all which it contains, whether
animate or inanimate? Yet such is indeed the fact. We are thus, in
a measure, prepared to find that the material which forms the great
solar clouds may turn out to be a substance not quite unknown to the
terrestrial chemist. Nay, further, its very abundance in the sun might
seem to suggest that this particular material might perhaps prove to
be one which was very abundant on the earth.
[Illustration: THE SUN'S CORONA.
From a photograph taken by Professor Schaeberle, at Mina Bronces,
Chili, in April, 1893, and kindly loaned by Professor E.S. Holden,
director of the Lick Observatory.]
I had occasion to make use of the word carbon in a lecture which
I gave a short time ago, and I thought when I did so that I was of
course merely using a term with whose meaning all my audience must be
well acquainted. But I found out afterwards that in this matter I had
been mistaken. I was told that my introduction of the word carbon had
quite puzzled some of those who were listening to me. I learned that a
few of those who were unfamiliar with this word went to a gentleman
of their acquaintance who they thought would be likely to know, and
begged from him an explanation of this mysterious term; whereupon he
told them that he was not quite sure himself, but believed that carbon
was something which was made out of nitro-glycerine! Even at the risk
of telling what every schoolboy ought to know, I will say that
carbon is one of the commonest as well as one of the most remarkable
substances in nature. A lump of coke only differs from a piece
of carbon by the ash which the coke leaves behind when burned. As
charcoal is almost entirely carbon, so wood is largely composed of
this same element. Carbon is indeed present everywhere. In various
forms carbon is in the earth beneath our feet, and in the air which we
breath. This substance courses with the blood through our veins; it is
by carbon that the heat of the body is sustained; and the same element
is intimately associated with life in every phase. Nor is the presence
of carbon merely confined to this earth. We know it abounds on other
bodies in space. It has been shown to be eminently characteristic of
the composition of comets. Carbon is not only intimately associated
with articles of daily utility, and of plenteous abundance, but with
the most exquisite gems of "purest ray serene." More precious than
gold, more precious than rubies, the diamond itself is no more than
the same element in crystalline form. But the greatest of all the
functions of carbon in the universe has yet to be mentioned. This same
wonderful element has been shown to be in all probability the material
which constitutes those glowing solar clouds to whose kindly radiation
our very life owes its origin.
[Illustration: At 10.34 A.M. The height of the eruption at this stage
was 135,200 miles.]
[Illustration: At 10.40 A.M. Height, 161,500 miles.]
[Illustration: At 10.58 A.M. Height, 280,800 miles.