_THE END OF MANY WORLDS._
A sign has recently appeared in the heavens which has been interpreted
in a way suggesting that many worlds like our own have undergone a
terrible catastrophe, every living creature upon them being consumed as
by fire. I propose briefly to consider some of the thoughts suggested by
this strange event.
It is difficult when we look at the star-lit heavens, suggestive as they
are of solemn peace, to conceive the stupendous energy, the fierce
uproar and tumult, of which even the faintest visible star in reality
tells us. Pythagoras spoke of the harmony of the celestial spheres,
which we are only prevented from hearing by its continuity. "There's not
the smallest orb which thou beholdest," said the science of the middle
ages,
"But in his motion like an angel sings,
Still quiring to the young-eyed cherubim."
The science of our own time tells us a still stranger story. There's not
the smallest orb which thou beholdest, she says, but in his motion
throbs like a mighty heart, still pulsating life to the worlds which
circle round it. But while our powers of vision are limited to the
narrow range of our present telescopes, we cannot watch the action of
these great centres of energy, nor can we hope that the uproar of those
remote fires will ever reach mortal ears, though to the mind's ear clear
and distinct. It is no longer a mere fancy that each star is a sun.
Science has made this an assured fact, which no astronomer thinks of
doubting. We know that in certain general respects each star resembles
our sun. Each is glowing like our sun with an intense heat. Around each,
as around our sun, are the vapours of many elements. In each the fires
are maintained, as they are maintained in our sun, in some way which may
be partly mechanical, partly chemical, but which certainly does not in
the least resemble combustion. We know that in each star processes
resembling in violence those taking place in our own sun must be
continually in progress, and that such processes must be accompanied by
a noise and tumult compared with which all the forms of uproar known
upon our earth are as absolute silence. The crash of the thunderbolt,
the bellowing of the volcano, the awful groaning of the earthquake, the
roar of the hurricane, the reverberating peals of loudest thunder, any
of these, or all combined, are as nothing compared with the tumult
raging over every square mile, every square yard, of the surface of each
one among the stars.
If we remember this when we hear of stars varying in brightness, we
shall perceive that the least change which could be recognised from our
remote stand-point must represent an accession or falling off of energy
corresponding to far more than all the energies existing on our earth,
or indeed on all the members of the solar system taken together.
Astronomers recognise our sun as in one sense a variable star; for we
can hardly suppose that he shines with the same degree of brilliancy
when many spots mark his surface as when he is quite free from spots;
and astronomers know that these changes in the sun's condition
correspond to wonderful changes in his activity. When spots are most
numerous, the coloured flames rage with fierce energy over his whole
globe, metallic vapours are shot forth from below his visible surface
with velocities of many miles per second. Whereas, when he has no spots,
the coloured flames sink down from their former height of tens of
thousands of miles, till they are but a few thousand miles in height;
while metallic vapours are seldom emitted, and never to the same height,
or with the same velocity, as when the spots are most numerous. But
though the sun thus varies in condition, and probably in his total
brightness, we cannot suppose that such variations could be recognised
from the distance of even the nearest among the fixed stars. What, then,
must be the nature of changes taking place in a star, that we, at our
enormous distance, should be able to recognise them! We may well believe
that the entire aspect of such a star must be changed to the
inhabitants, if such there are, of worlds circling around them.
If, however, the changes taking place in stars, whose variations of
brightness can just be recognised, must be amazing, how stupendous must
be the changes affecting a star which alternates from brightness to
invisibility, like Mira, the Star Wonderful, in the constellation of the
Whale! how destructive those affecting a star like Eta, of the ship
Argo, which has varied from the fourth magnitude to a lustre nearly
equalling that of Sirius, and thence to the lowest limit of visibility,
in the course of the last hundred years!
Even these changes, however, though justly regarded as among the chief
wonders and mysteries of the star-depths, seem in turn to sink into
nothingness by comparison with the sudden appearance of a new star, as
interpreted by modern scientific observations. Of old, when a new star
appeared, it was thought for awhile to be a fresh creation; a new sun
set in the centre of a new system of worlds,--a thought which was not
then so startling as in our own times it would be reckoned. When the new
star was seen slowly to die out until at last it became invisible, men
were content to regard it as a sign set in the heavens for a special
purpose. Nor did they find much difficulty in associating such a
phenomenon with some event of importance occurring during its
continuance, or soon after the new star had died out. Such were the
explanations offered respecting the exceedingly bright star which made
its appearance in the constellation Cassiopeia in the year 1572. The
place in which it appeared is shown in fig. 7. It must have sprung into
its full glory in a very short time, for Tycho Brahé, the celebrated
astronomer, tells us that, returning on November 1, 1572, from his
laboratory to his dwelling-house, he saw the new star, which he was
certain had not been visible an hour before, shining more brightly than
any before seen. It surpassed all the stars in the heavens in
brilliancy, and even Jupiter when that planet is at its brightest. Only
Venus at her brightest was superior to the new star. For three weeks it
shone with full lustre, after which it began slowly to decline. Being
situated in a part of the heavens always above the horizon (for
European observatories), the star's entire history could be followed. It
remained for sixteen months steadfast in its position like the other
stars. As it decreased in size it varied in colour. "At first," says an
old writer; "its light was white and extremely bright; it then became
yellowish; afterwards of a ruddy colour like Mars; and finished with a
pale, livid white, resembling the colour of Saturn."
[Illustration: Fig. 7.--Cassiopeia; showing where a new star appeared in
the year 1572.]
In passing it may be remarked that there are reasons for expecting the
return of Tycho Brahé's star in the course of a few years. For other
new stars have been recorded as seen in the same part of the heavens in
the years 945 and 1264, and though the interval from 945 to 1264 (or 319
years) exceeds by 11 years the interval from 1264 to 1572 (or 308
years), yet the difference is but small by comparison with either entire
interval; and we may not unreasonably believe that the three new stars
seen in Cassiopeia have been only three apparitions of one and the same
star, which shines out, with superior lustre, for a few months, once in
a period averaging about 313 years. It seems to me not at all unlikely
that, some time during the next twenty years, astronomers will have an
opportunity of examining, with the telescope and spectroscope, a star
which last appeared before either instrument had been invented.
Already facts are known respecting the so-called new stars which will
not permit us to accept the explanations of old so readily offered and
admitted, simply because so little was certainly known.
In the year 1866 a star appeared suddenly in the constellation of the
Northern Crown, where no star had before been visible to the naked eye.
It was a little below the arc of stars forming the celestial coronet.[7]
It shone as a second magnitude star when first seen, but very rapidly
diminished in lustre. It increased our knowledge in two important
respects.
First, on examining Argelander's charts of the northern heavens, the new
star was found to have been observed and charted as a tenth magnitude
star, that is, four magnitudes below the lowest limit of naked eye
vision. It was not, then, a new sun, though it might still truly be
called a new star, in this sense, that it was a new member of the set of
stars which adorn our skies as seen by ordinary vision.
In the second place, the star was subject to the searching scrutiny of
spectroscopic analysis, with results of a most interesting character.
The reader is no doubt aware that when the light of a star is analysed
into its component colours by the instrument called the spectroscope, it
is found that all the colours of the rainbow are present, as in the case
of solar light, but (also in the sun's case) not all the tints of these
colours. Certain dark lines athwart the rainbow-tinted streak, called
the _spectrum_ of the star, indicate the presence of absorbing vapours
in the star's atmosphere. This general statement is true of every fixed
star, though the dark lines of some stars differ in number and position
from the dark lines of others, showing that other absorbing vapours are
present. In the case of the new star in the Crown, the usual stellar
spectrum was shewn,--a rainbow-tinted streak crossed by a number of dark
lines. But besides these, there were seen four very bright lines,--lines
so bright that the rainbow-tinted streak appeared as a dark background.
The meaning of this is well understood by spectroscopists. It signifies
that besides the vapours which, being cooler than the star, absorbed a
portion of its light, and produced the dark lines, some vapours were
present in the star's atmosphere which were a great deal hotter than the
star, and so produced bright lines. Now two of the lines corresponded in
position with two of the well known lines of the gas hydrogen, showing
that this was one of the gases which had been raised to an unusual
degree of heat.
It was inferred that there had been some tremendous disturbance in that
remote star, by which the hydrogen and some other vapours present in its
atmosphere had been intensely heated. But astronomers were unable to
decide whether the disturbance was of the nature of a conflagration, the
hydrogen actually burning, or whether the heat was occasioned in some
other way, as by the downfall of some immense mass upon that remote
sun. For burning hydrogen and glowing hydrogen, though either could give
the observed bright lines, are very different things. In the former case
a chemical change is taking place, as in the case of burning wood or
coal; the latter case resembles that of redhot iron, which is not
burning itself (not changing into a different form as everything does
which burns), though it will burn other things,--in the ordinary, and
incorrect, use of the expression.
The general belief was that there had been a downfall of matter on the
star in the Crown, by which the whole globe of that sun had been excited
to an intense degree of heat, especially at the surface, near which lies
the hydrogen atmosphere of the star.
I must leave, however, to the next part, the further consideration of
the strange thoughts suggested by the outburst of this star. I wish to
use the small space remaining at present to indicate the place where
another new star burst forth last November, so that any readers of these
pages who have telescopes may know where to look for a sun which is now
dying out, but was shining a few weeks ago as a third magnitude star.
Fig. 8 presents a portion of the well-known constellation Cygnus or the
Swan. Any star atlas will indicate the place of the lettered stars shown
in the figure. The constellation itself does not show at all well at
this season of the year.[8] The part shown in the figure is close to the
horizon, and directly under the pole-star, at about half-past ten in the
middle of February; but a little higher up, between north and
north-east, at midnight. Professor Schmidt, of the Athens Observatory,
noticed a new star, in the place shown, on November 24th last. It must
have shone out suddenly, for Schmidt had been observing in that region
on the night of November 22nd (the last preceding clear night). It has
since gradually faded, until now a small telescope is required to show
it, shining as a seventh magnitude star, with a well-marked orange tint.
[Illustration: Fig. 8.--Part of Cygnus, showing the place of new star
(November 24, 1876).]
We have now to consider the history of this star, and discuss the
general questions suggested by the sudden blazing out of suns which had
for many years, and probably for many centuries, shone continuously with
a far feebler lustre. It is clear that we have good reason to be
interested in these questions, seeing that, for aught we know, our sun
may be one of those exposed to sudden great increase of lustre.
* * * * *
It seems certain, in the first place, that this star leapt very suddenly
to its full splendour. Schmidt had been observing the same regions of
the heavens only two evenings before, and is sure the star was not then
shining visibly to the naked eye. Again, astronomy is now studied by so
many persons, and so many more who are not students of astronomy are now
well acquainted with the constellations, that it is very difficult for a
new star to shine many hours without being detected. For example, the
new star in the Crown, which appeared in May, 1866, though not so well
placed for observation, was detected by many observers at widely distant
stations within a few hours of each other. It is probable that the star
acquired its full lustre in a few hours at the utmost, and quite
possible that, had any one been watching the place where the star
appeared, he would have been able to see the star grow into full
brightness by visible change of lustre, just as the lustre of a
revolving light in a distant lighthouse visibly waxes and wanes. It may
be, of course, that the increase of the star from its ordinary lustre,
up to the stage when first it was visible to the naked eye, occupied
many days, or even many months or years; but it seems more likely that
as the later stages of increase were rapid, so also was the entire
development of the new lustre. In that case, if there were inhabited
worlds circling around that remote sun, they had but brief warning of
the fate in store for them, as presently to be described.
Like the star in the Northern Crown, the new star in Cygnus was
subjected to the searching scrutiny of the spectroscope. The results,
though similar in general respects, were even more interesting than in
the case of the brighter new star. In the interval between 1866 and 1876
spectroscopic analysis has developed largely. It has thus become
possible to analyse more completely the light even of faint stars than
the light of bright stars could be analysed a decade of years since.
The spectrum of the new star as examined by M. Cornu, of the Paris
Observatory, showed the bright lines of hydrogen, indicating the
presence of enormous quantities of glowing hydrogen, in a state of
intense heat. But beside these bright lines, others also could be seen.
One of these was an orange-yellow line. It will be understood that the
faint spectrum of a star cannot be so readily lengthened by increasing
the dispersion as a bright spectrum; for with too great dispersion the
light fades out altogether. And though this is not strictly the case
with the bright lines, which are merely thrown farther apart by
dispersion, yet still it remains true that one cannot deal with a star
spectrum even of bright lines as one can with the solar spectrum. So
that M. Cornu was not able to determine whether the orange-yellow line
belonged to sodium, or to that other substance, whatever it may be,
which produces the orange-yellow line seen in the spectrum of a solar
prominence.[9] Another bright line, green in colour, agreed in position
with a triple line belonging to the metal magnesium. Lastly, a bright
yellowish-green line was seen, which is known to be present in the
spectrum of the sun's corona and of the low-lying ruddy matter round the
sun, called the _sierra_ by some, and by others (apparently unfamiliar
with the Greek language) the chromosphere.
Now all this agrees very well with what had been noticed in the case of
the star in the Northern Crown. For, unquestionably, if a sun increases
so much in heat and lustre that the hydrogen outside it glows more
brightly than the body of the star, then other matter _outside_ that sun
might also be expected to share the great increase of heat. We see that,
outside our own sun, hydrogen, a certain unknown vapour of an orange
yellow colour, magnesium, and another unknown vapour of greenish-yellow
colour are present in enormous quantities; and it seems, therefore,
reasonable to believe that other suns have these gases extending far
outside the rest of their substance. It is certain that, if our sun were
caused to glow with far more than its present degree of heat, the gases
whose increase of brightness would be most discernible from a distant
station (as a world circling around some remote star) would be just
those gases which were glowing so resplendency around the star in Cygnus
last November--or rather at the time when that light which reached us
last November set out from the remote star in the Swan.
When we view the outburst of that remote sun in this way the thoughts
suggested are not altogether satisfactory. That sun shows far too much
resemblance to our own, and behaved, so far as can be judged, far too
much as our own sun would behave if roused to many times its present
degree of heat and splendour. When we hear of a railway accident it is a
matter of special interest to us (if we travel much) to learn whether
the conditions under which the accident took place resembled those under
which the trains proceed by which we chiefly travel. When an express
train suffers in such a way as to show some special danger arising from
great velocity, we find ourselves to some degree concerned personally in
the investigation which follows, if we travel generally by quick trains.
If a bridge breaks down, and we have often to traverse bridges in
railway journeying, we are similarly concerned, especially if any of the
bridges we have to cross resemble in structure the one which has given
way. So also of many other special forms of danger in railway
travelling. Now, on the same principle, we cannot but regard with
considerable interest the circumstance that, apparently, a catastrophe
has taken place in the star in Cygnus, which has not only affected a sun
resembling our own very closely in constitution, but has produced
effects very closely corresponding to those which would affect our own
sun if, through any cause, he were excited to many times his present
degree of heat.
Let us pause a little to reflect upon the effects which would follow a
great increase of the sun's lustre. A change in our own sun, such as
affected the star in Cygnus, or that other star in the Northern Crown,
would unquestionably destroy every living creature on the face of this
earth; nor could any even escape which may exist on the other planets of
the solar system. The star in the Northern Crown shone out with more
than 800 times its former lustre: the star in Cygnus with from 500 to
many thousand times its former lustre, according as we take the highest
possible estimate of its brightness before the catastrophe, or consider
that it _may_ have been very much fainter. Now, if our sun were to
increase tenfold in brightness, all the higher forms of animal life and
nearly all vegetable life would inevitably be destroyed on this earth. A
few stubborn animalcules might survive, and, possibly, a few of the
lowest forms of vegetation, but naught else. If the sun increased a
hundredfold in lustre his heat would doubtless sterilise the whole
earth. The same would happen in other planets. The heat falling on the
remotest members of the solar system would not, indeed, be excessive
according to our conceptions. But if we regard Neptune, Uranus, Saturn,
and Jupiter as the abode of life (which, for my own part, I consider
altogether improbable), we cannot but suppose the orders of living
creatures in each of these planets to be well fitted to exist under the
conditions subsisting around them. If this is so--as who can for a
moment doubt?--a sudden enormous increase in the sun's heat, though not
making the supply received by those planets much greater than, or even
equal to, the supply which we receive from the sun, would prove as fatal
to living creatures there as to living creatures on our earth.
If, then, the sun increased in splendour as the stars have increased
which the astronomers call new stars or temporary stars, there would be
an end of life upon this earth; and nothing short of either the
spontaneous development of life, or of the creation of various forms of
life, could people our earth afresh. Science knows nothing of
spontaneous generation, and believers in revelation reject the doctrine.
Science knows nothing of the creation of living forms, but believers in
revelation accept the doctrine. Certain it is that if our sun ever
undergoes the baptism of fire which has affected some few among his
brother suns, one or other of these processes (if creation can be called
a process) must come into operation, or else our earth and her companion
worlds would for ever after remain absolutely devoid of life.
But if our sun, without suffering so great a change, underwent a change
of less degree, it might well happen that though there would be enormous
destruction of life upon the earth and other planets, some life
(presumably the strongest and best) would survive. In that case, after a
long period of time, the earth would again be well peopled, and it might
even be that the various races of terrestrial creatures would be
improved, by the desolation which the great solar conflagration had
wrought.
It is somewhat curious, considering how little there is in the ordinary
progress of events to suggest the idea, that most of the ancient systems
of cosmogony recognised the periodical destruction of living creatures
on the earth by fire as well as by water. Each form of destruction was
supposed to be brought about by planetary influences. The Ecpyrosis, or
destruction by fire, was effected when all the planets were in
conjunction with Cancer; the Cataclysm, or destruction by flood, when
all the planets were in conjunction with Capricorn. Each form of
destruction was supposed also to purify the human race. "Towards the
termination of each era," writes Lyell, speaking of these old ideas,
"the gods could no longer bear with the wickedness of men, and a shock
of the elements or a deluge overwhelmed them; after which calamity
Astrea again descended on the earth, to renew the golden age." The
Greeks undoubtedly borrowed all such doctrines from the Egyptians, who
"believed the world to be subject to occasional conflagrations and
deluges, whereby the gods arrested the career of human wickedness, and
purified the earth from guilt. After each regeneration mankind was in a
state of virtue and happiness, from which they gradually degenerated
again into vice and immorality."
Considering that we have every reason to believe the records of great
floods to relate to events which actually occurred, however imperfectly
remembered, it seems not unreasonable to believe that the tradition of
great heats had its origin in observed phenomena. As neither ordinary
conflagrations nor volcanic outbursts would have suggested traditions of
the kind, it would seem not impossible that at certain times our sun may
have acquired for a time unusual lustre and heat, causing great and
widely spread destruction among all forms of animal and vegetable life.
This idea may possibly seem to many, especially at a first view, too
wild to be entertained for a moment. Our sun shines, so far as appears
to ordinary observation, with steadfast lustre from year to year, and
also from age to age. If an occasional hot season suggests for a while
to some that the sun has grown hotter, or a cool season that he has
grown cooler, the restoration of cool or warmer weather, as the case may
be, causes the thought to be quickly cast on one side that a change of
either kind has taken place. Again, if we examine the historical records
of past ages, we find little to suggest the idea, or even the
possibility, that the sun in former times shone with greater splendour
or with less than at present. The men of those days were formed like the
men of our own day, and could not have supported any much greater degree
of heat or of cold than men can support at present. Any sudden accession
(or diminution) of solar light and heat, such as we are considering,
would certainly have attracted marked attention, and have been recorded
for the benefit of future ages. The geologic record, again, does,
indeed, suggest variations in the sun's emission of heat as constituting
one among the few available explanations of the existence of tropical
forms of life in certain strata and of arctic forms in other strata. But
even if this explanation be the true one, which is by no means
established, such variations must of necessity have been slow, the
condition of increased heat continuing for many ages in succession, and
the like with the condition of diminished heat. We have no evidence,
historical or geological, of the occurrence of any sudden accession of
solar heat, followed by a quick return to the normal temperature, unless
we find such evidence in the tradition prevalent among Egyptian, Indian,
and Chinese cosmogonists, that at certain recurring epochs in the past
our earth has undergone destruction and renovation by fire.
Yet, as I shall now show, it appears that the one only natural
interpretation which can be given of the outburst of a new or temporary
sun indicates an event which might happen to our own sun, and an event
which if it happened at all would happen periodically. Moreover, while
it will appear that there is no reason for fearing the possible
occurrence (which would, in such case, be really the recurrence) of such
a catastrophe in the case of our own sun as has affected the stars in
the Crown and in Cygnus, there is no reason for rejecting as incredible
the idea that catastrophes very serious in their character may have
affected our sun; and there is abundant reason for believing that
_small_ alterations in the sun's total emission of light and heat take
place very often, in some cases periodically; in others--so far as we
can yet judge--periodically.
Lastly, it will be seen that there is always a possibility that our own
or any other sun may undergo precisely such a change as the stars in
Cygnus and the Northern Crown. Some indeed, even among men of science
(as the Abbé Moigno, for example) believe that it was an event of this
sort which St. Peter predicted when he wrote, that as the old world,
being overflowed with water, perished, so "the heavens and the earth
which are now, by the same word are kept in store, reserved unto fire."
According to that view, the day of destruction will come "as a thief in
the night; in the which the heavens shall pass away with a great noise,
and the elements shall melt with fervent heat, the earth also, and the
works that are therein shall be burned up."
* * * * *
Let us consider how the sudden brightness of a new star may be
explained.
I must confess that for my own part I do not attach much weight to the
suggestion once made by Mr. Huggins, that an actual conflagration had
taken place in the case of the new star in the Northern Crown. It does
not seem to me that any process of mere burning could account for the
enormous accession of light and heat which that sun underwent.
Consider the case of our own sun. His heat is very far beyond that which
would be given out by any matter known to us undergoing any known
process of true combustion. That is to say, if a mass as large as the
sun of any known substance were caused to burn, under any conditions we
can imagine, the momentary emission of heat by that mass would be very
much less than the momentary emission of heat by the sun.
Now it is quite conceivable that by some great accession of combustible
matter, some supply of fuel exceeding many times his entire mass, the
sun's entire emission of heat might be very largely increased. But
though such an idea is conceivable, it seems altogether far-fetched. The
conception is, in fact, inadmissible as an explanation of the increase
of heat of a temporary star, not because of the improbability of the
sudden accession of so enormous a quantity of matter (though that
improbability is very great), but because if so enormous a quantity of
matter fell upon the sun, many times as much heat would be generated by
the mechanical effect of the impact as by the combustion of the freshly
received matter. So that even with the daring assumption here made,
combustion would account for only a small portion of the increase of
light and heat.
Huggins' idea was indeed somewhat different. He supposed that in
consequence of some great internal convulsion of the sun in the Northern
Crown a large volume of hydrogen and other gases was evolved from the
interior, the hydrogen then by burning giving out the light
corresponding to the bright lines. At the same time, the mass of the sun
would be intensely heated by the surrounding mass of glowing hydrogen.
When the liberation of gas from the interior ceased the flame would die
out, and the sun's surface would gradually cool. But if we judge by the
case of our own sun, the heat of the _burning_ hydrogen would be nothing
near so great as the heat of the glowing hydrogen already outside and
within the visible globe of a sun.
On the whole it seems altogether more probable that the accession of
splendour observed in the case of temporary stars is due to the downfall
of enormous masses of matter upon the surface of these suns. It is, no
doubt, well known to most of my readers that the downfall of meteoric
matter upon the surface of our own sun has been considered a sufficient
explanation of the sun's entire emission of light and heat. The theory
that the sun's heat and light _are_ thus excited has long since been
abandoned; but not because the cause would be insufficient. It has been
abundantly proved that a downfall of meteors, not sufficient in quantity
to add appreciably to the sun's size in many thousands of years, would
generate more heat and light than he emits in that time. The meteoric
theory has been abandoned simply because it has been shown that no such
downfall is taking place.
The reason why meteoric impact would suffice to warm the sun to his
present temperature if the meteoric showers were heavy, and to warm him
far beyond his present temperature if for a few days very heavy
meteoric showers fell upon him, is simply that his attraction upon
matter approaching him from without is capable of generating a
tremendous velocity. We know that when a cannon-ball strikes a metal
target, with a velocity perhaps of some 400 yards per second, great heat
is excited, and there is a momentary flash of light. If the velocity
were doubled, the quantity of heat would be doubled also. Conceive,
then, the tremendous heat which would be excited if a cannon-ball could
be caused to strike a target with a velocity exceeding that just named
some 1500 times! The ball and target would both be vaporised by the
shock, if--which, however, could never happen--the target resisted the
blow and brought the ball to rest. Now matter which reaches the sun from
without, under the influence of his tremendous attraction, strikes his
globe with a velocity 1500 times greater than that of a cannon ball
striking a target at a distance of two or three hundred yards. The heat
excited is, therefore, very intense; and if meteors were showering at
all times and in dense flights upon the sun's surface, we should require
no other explanation of the sun's heat.
But it appears that meteoric systems are neither so numerous nor so rich
as to account for the sun's uniform emission of heat, though occasional
meteoric showers upon the sun may be heavy enough to increase
appreciably the amount of heat he emits. It would seem, from
experiments which have been made by Professor Piazzi Smyth, of the
Edinburgh Observatory, and later by the Astronomer Royal at Greenwich,
that from time to time the sun's emission of heat really is greater than
usual. It seems not at all improbable that the increase is due to the
occasional fall of large masses of meteors in great numbers upon the
sun.
Again, it seems that such falls occur periodically, or rather that at
regular intervals great meteoric streams pour upon the sun's surface.
For instance, the periodic increase and decrease in the number of
sun-spots is accompanied (so far as we can judge by the observations
made at Edinburgh and Greenwich) by an accession and diminution of the
solar heat; and if the change is attributed to the passage of a meteoric
stream athwart the sun, we should have to assign to such a stream a
period of rather more than eleven years. This, from what we know about
the association between meteors and comets, would correspond simply to
the existence of a comet whose path intersects the sun's globe, and
which is followed by a train of millions of large meteoric masses, many
of which are consumed at each passage of the rich portion of the train
athwart the globe of the sun. This comet must of necessity be
inconspicuous, since it has hitherto escaped detection. In fact, its
head and nucleus must long since have been entirely destroyed. Only the
meteoric train, far more widely scattered, remains, simply because at
each passage past the sun, though many are captured, far greater numbers
get safely past.
I am careful to remind the reader that though I have, for convenience,
used the indicative mood in describing these matters, I am in reality
presenting merely a theory. It may be that the solar spots and the
accessions of heat are produced in some other way. But I must admit I
find strong reasons for regarding as probable the general theory, that
the alternations of solar activity (not the solar activity itself be it
noted) are excited from without. And since we know, as a matter of fact,
that meteors exist in enormous numbers within the solar system, and that
they aggregate with rapidly increasing density in the sun's
neighbourhood, we must believe that they fall upon the sun in enormous
numbers. We also perceive that the supply cannot be uniform, but must
vary greatly from time to time; while what we know about the periodicity
of meteoric showers on our own earth suggests the belief, we may almost
say the certainty, that there must be periodic downfalls of very heavy
meteoric showers upon the sun's surface. We have, then, strong
probability in favour of the belief that events may occur which, _if_
they occurred, might be expected, with a high degree of probability, to
produce effects resembling those actually observed,--viz., the
production of a heat more intense than usual, accompanied by signs of
great disturbance like the sun-spots. It does, therefore, seem at least
not improbable that these accessions of heat and these signs of great
disturbance really are brought about in the way supposed.
A further argument in favour of the meteoric origin of solar
alternations of heat is to be found in the fact that, on one occasion at
least, a solar phenomenon, corresponding precisely to what we should
expect to see, if great meteoric masses fell upon the sun, has been
followed by precisely the same signs of terrestrial disturbance which
accompany and follow the formation of great solar spots. I refer to the
remarkable occurrence witnessed by Carrington and Hodgson (at different
observatories) in September, 1859, when two intensely bright points of
light were seen travelling beside each other at the rate of about 120
miles per second along a short arc of the sun's surface,--an arc only
equal in length to some four-and-a-half times the diameter of our earth.
On that occasion the emission of solar heat may or may not have been
increased in an appreciable degree for several minutes. My own belief is
that it must have been; but we certainly have no means of proving that
it was. What we do know certainly is, that on that day all the
phenomena which usually accompany the existence of many and large
sun-spots showed themselves with exaggerated intensity. The magnetic
needle was greatly disturbed, auroras displayed their coloured streamers
in both hemispheres, telegraphic communication was interrupted, and
everything tended to show that a disturbance of the same general
character as that which produces sun-spots, but much more active while
it lasted, had affected the sun. It seems, then, altogether reasonable
to infer that sun-spots are due to the same cause as the disturbance
which then occurred. So that if we conclude, with most astronomers
competent to form an opinion, that the disturbance witnessed by
Carrington and Hodgson was due to the downfall of two very large
meteoric masses upon the sun, it would follow that sun-spots are due to
more wide-spread meteoric showers, not consisting of masses so large.
The reader will long since have guessed, no doubt, to what all this
tends. If the periodical variations of the sun's surface are due to
meteoric and cometic systems whose orbits intersect the sun's globe,
their periods being short (that is, lasting but a few years), it may
well be that more important meteoric and cometic systems intersecting
the sun's globe exist, which have much longer periods. When next one of
these makes its passage athwart the sun, far more important solar
disturbances may take place than those which occur when the regularly
recurring systems salute the sun. Two or three times in the history of
science comets have approached very close to the surface of the sun, as
in 1680, and again in 1843, but without actually impinging upon it. Very
slight changes in the motions of those comets, owing to the disturbing
influences of the planets, would cause their very nuclei to strike the
sun, and their meteoric trains to pour afterwards in a full stream upon
him for many days, or even for many months and years in succession.
Now I do not think our sun would necessarily suffer very much from any
of these known comets. They may long since have parted with the greater
quantity of their substance. But it is quite possible that even one of
those well-known comets of the solar system might cause very serious
outbursts of solar heat and light; and it is certainly not only possible
but extremely probable that other comets, such as have visited the solar
system on paths fortunately not bringing them near to the sun, would
have worked much mischief had their paths been differently situated.
We know that Newton held this opinion. He considered the real danger
from comets to reside, not in the possibility that one might strike our
earth, but in the possibility that one, falling upon the sun, might
excite that orb to a degree of heat so intense that all life on this
earth would be destroyed. It is true that, in Newton's time, physical
laws were not so well understood as at present, and a considerable
portion of Newton's reasoning was consequently inexact. But nothing
which is now known opposes itself to the belief which Newton adopted on
this subject. On the contrary, whereas Newton only recognised the danger
arising from the consumption of a comet as fuel for the sun, we now
recognise a far more serious danger, from the force of meteoric impact,
and the heat excited as the thermal equivalent of the destroyed
velocities. Of this part of the danger Newton had no clear conception,
the relations between mechanical energy and heat not having been
established until quite recent times.
It appears to me, however, that the danger in the case of our own
sun--or may we not say _our_ danger?--arises only from the possibility
that some one of the comets which visit us from the star-depths may make
straight for the sun; and this danger is exceedingly small. Almost
certainly a comet which, leaving the domain of another sun, falls under
the attractive influence of our own, would approach him on a path
passing many millions of miles from his surface. The chances against a
more direct approach are so great that they may be regarded as, to all
intents and purposes, overwhelming. A comet _might_ visit us from the
star-depth on a destructive course, just as a single black ball _might_
be drawn at the first trial from a bag containing a million white balls
and only that single black one. But the danger is exceedingly small.
We see, indeed, that other suns have suffered in this way, assuming
cometic downfall to be the true cause of stellar outbursts. There are so
many millions of suns, however, in the region of space to which
telescopic survey extends that the occurrence of ten or twelve such
outbursts in the course of four or five centuries need not be regarded
as implying any serious danger. Moreover, all the suns which have thus
suffered lie within a particular region of the heavens,--viz., in the
Milky Way, and in that half of the Milky Way which is most irregular,
one may almost say _ragged_, in structure. (With one exception--the star
in the Northern Crown, which, nevertheless, lies on a faint outlying
streamer of the Milky Way not discernible to ordinary vision.) If then
our sun belongs to this region of space, the danger for him and for us
is somewhat greater than my previous argument would indicate. For, in
that case, we must compare the number of outbursts, not with the total
number of stars within telescopic range, but with the number of those
stars which lie within this particular region of space. On the other
hand, if our sun does not lie within that region of space, the danger
for him and for us is very much less; for instead of a certain small
number of accidents among his fellow suns, there have been no such
accidents, only accidents affecting other suns which must be differently
classed.
The case may be compared to the estimation of the dangers, let us say,
of travelling by ocean steamships on a particular route. If we take the
total number of accidents, for instance, to steamships travelling
between England and the United States, we should estimate the risk of
the journey as very small, the number of passengers who have lost their
lives being very small compared with the number who have made the
journey. But even this small risk is diminished if we estimate the
danger for a passenger by Cunard steamships, simply because no passenger
has yet lost his life through accident to one of these Cunard vessels.
So in the case of our sun, the danger of an outburst such as has
affected the stars in the Northern Crown and Cygnus is small enough when
we estimate it by comparing the number of such accidents with the total
number of stars, but vanishes almost into nothingness when we note that
no insulated star like our sun seems hitherto to have undergone one of
these tremendous catastrophes.
But as regards the fate of worlds circling round suns which have
suffered in this way, we can form but one opinion. Beyond all doubt, if
such worlds existed and were inhabited when their central orb blazed
forth with many hundred times its former lustre, all life must have
perished from their surface. We may believe, as many do, that no
conditions are too unlike those we are familiar with on earth to render
life impossible; that the creatures subsisting in a world exposed to the
most fiery heat or to the most intense cold are adapted as perfectly to
the conditions under which they subsist as we are to the circumstances
of terrestrial life. But even adopting this view, though it seems to
accord ill with what we know of our own earth,--where life ceases
towards the polar and over large tracts of the equatorial regions,--we
could not believe that creatures thus adapted to the conditions
prevailing around them could endure an entire change of those
conditions. With the accessions of heat in the stars in Cygnus and the
Crown, such change must inevitably have taken place. Therefore, as I
think, we must regard the catastrophes affecting those remote suns as
assuredly involving "The End of many Worlds."
_Note._--What is stated in the latter portion of this chapter
applies now only to the star in the Northern Crown; for the star in
Cygnus has not faded into a small star, but into a small nebula! For
the further history of this star, the reader is referred to my
forthcoming treatise entitled, "Pleasant Ways in Science."