occurred in 1883, and it will be remembered that the air-wave started
by the explosion was felt around the globe, and that, probably owing
to the dust and water-vapor blown into the atmosphere, the sunsets
even in America became of that extraordinary crimson we all remember
three years ago; and coincidently, that dim reddish halo made its
appearance about the sun, the world over, which is hardly yet gone.[6]
Very careful estimates of the amount of ashes ejected have been made;
and though most of the heavier particles are known to have fallen
into the sea within a few miles, a certain portion--the lightest--was
probably carried by the explosion far above the lower strata of the
atmosphere, to descend so slowly that some of it may still be there.
Of this lighter class the most careful estimates must be vague; but
according to the report of the official investigation by the Dutch
Government, that which remained floating is something enormous. An idea
of its amount may be gained by supposing these impalpable and invisible
particles to condense again from the upper sky, and to pour down on
the highest edifice in the world, the Washington Monument. If the dust
were allowed to spread out on all sides, till the pyramidal slope was
so flat as to be permanent, the capstone of the monument would not only
be buried before the supply was exhausted, but buried as far below the
surface as that pinnacle is now above it.
[6] In January, 1887.
Of the explosive suddenness with which the mass was hurled, we can
judge something (comparing small things with great) by the explosion of
dynamite.
It happened once that the writer was standing by a car in which some
railway porters were lifting boxes. At that moment came an almost
indescribable sound, for it was literally stunning, though close and
sharp as the crack of a whip in one’s hand, and yet louder than the
nearest thunder-clap. The men leaped from the car, thinking that one of
the boxes had exploded between them; but the boxes were intact, and we
saw what seemed a pillar of dust rising above the roof of the station,
hundreds of yards away. When we hurried through the building, we
found nothing on the other side but a bare plain, extending over a
mile, and beyond this the actual scene of the explosion that had
seemed to be at our feet. There had been there, a few minutes before,
extensive buildings and shops belonging to the railroad, and sidings
on which cars were standing, two of which, loaded with dynamite, had
exploded.
[Illustration: FIG. 78.--VESUVIUS DURING AN ERUPTION.]
Where they _had_ been was a crater-like depression in the earth, some
rods in diameter; the nearest buildings, great solid structures of
brick and stone, had vanished, and the more distant wooden ones and the
remoter lines of freight-cars on the side-tracks presented a curious
sight, for they were not shattered so much as bent and leaning every
way, as though they had been built of pasteboard, like card-houses,
and had half yielded to some gigantic puff of breath. All that the
explosion had shot skyward had settled to earth or blown away before
we got in sight of the scene, which was just as quiet as it had been a
minute before. It was like one of the changes of a dream.
Now, it is of some concern to us to know that the earth holds within
itself similar forces, on an incomparably greater scale. For instance,
the explosion which occurred at Krakatao, at five minutes past ten, on
the 27th of August, 1883, according to official evidence, was heard
at a distance of eighteen hundred miles, and the puff of its air-wave
injured dwellings two hundred miles distant, and, we repeat, carried
into the highest regions of the atmosphere and around the world matter
which it is at least possible still affects the aspect of the sun
to-day from New York or Chicago.
Do not the great flames which we have seen shot out from the sun
at the rate of hundreds of miles a second, the immense and sudden
perturbations in the atmosphere of Jupiter, and the scarred surface of
the moon, seem to be evidences of analogous phenomena, common to the
whole solar system, not wholly unconnected with those of earthquakes,
and which we can still study in the active volcanoes of the earth?
If the explosion of gunpowder can hurl a cannon-shot three or four
miles into the air, how far might the explosion of Krakatao cast its
fragments? At first we might think there must be some proportionality
between the volume of the explosion and the distance, but this is not
necessarily so. Apart from the resistance of the air, it is a question
of the velocity with which the thing is shot upward, rather than the
size of the gun, or the size of the thing itself, and with a sufficient
velocity the projectile would never fall back again. “What goes up
must come down,” is, like most popular maxims, true only within the
limits of ordinary experience; and even were there nothing else in the
universe to attract it, and though the earth’s attraction extend to
infinity, so that the body would never escape from it, it is yet quite
certain that it would, with a certain initial velocity (very moderate
in comparison with that of the planet itself), go up and _never_ come
back; while under other and possible conditions it might voyage out
into space on a comet-like orbit, and be brought back to the earth,
perhaps in after ages, when the original explosion had passed out of
memory or tradition. But because all this is possible, it does not
follow that it is necessarily true; and if the reader ask why he should
then be invited to consider such suppositions at all, we repeat that
in our journey outward, before we come to the stars, of which we know
something, we pass through a region of which we know almost nothing;
and this region, which is peopled by the subjects of conjecture, is
the scene, if not the source, of the marvel of the falling stones,
concerning which the last century was so incredulous, but for which
we can, aided by what has just been said, now see at least a possible
cause, and to which we now return.
Stories of falling stones, then, kept arising from time to time during
the last century as they had always done, and philosophers kept on
disbelieving them as they had always done, till an event occurred which
suddenly changed scientific opinion to compulsory belief.
On the 26th of April, 1803, there fell, not in some far-off part of the
world, but in France, not one alone, but many thousand stones, over
an area of some miles, accompanied with noises like the discharge of
artillery. A committee of scientific men visited the spot on the part
of the French Institute, and brought back not only the testimony of
scores of witnesses or auditors, but the stones themselves. Soon after
stones fell in Connecticut, and here and elsewhere, as soon as men were
prepared to believe, they found evidence multiplied; and such falls,
it is now admitted, though rare in any single district, are of what
may be called frequent occurrence as regards the world at large,--for,
taking land and sea together, the annual stone-falls are probably to be
counted by hundreds.
It was early noticed that these stones consisted either of a peculiar
alloy of iron, or of minerals of volcanic origin, or both; and the
first hypothesis was that they had just been shot out from terrestrial
volcanoes. As they were however found, as in the case of the
Connecticut meteorite, thousands of miles from any active volcanoes,
and were seen to fall, not vertically down, but as if shot horizontally
overhead, this view was abandoned. Next the idea was suggested that
they were coming from volcanoes in the moon; and though this had
little to recommend it, it was adopted in default of a better, and
entertained down to a comparatively very recent period. These stones
are now collected in museums, where any one may see them, and are to be
had of the dealers in such articles by any who wish to buy them. They
are coming to have such a considerable money value that, in one case
at least, a lawsuit has been instituted for their possession between
the finder, who had picked the stones up on ground leased to him, and
claimed them under the tenant’s right to wild game, and his landlord,
who thought they were his as part of the real estate.
Leaving the decision of this novel law-point to the lawyers, let us
notice some facts now well established.
The fall is usually preceded by a thundering sound, sometimes followed
or accompanied by a peculiar noise described as like that of a flock
of ducks rising from the water. The principal sound is often, however,
far louder than any thunder, and sometimes of stunning violence. At
night this is accompanied by a blaze of lightning-like suddenness and
whiteness, and the stones commonly do not fall vertically, but as if
shot from a cannon at long range. They are usually burning hot, but
in at least one authenticated instance one was so intensely cold that
it could not be handled. They are of all sizes, from tons to ounces,
comparatively few, however, exceeding a hundred-weight, and they
are oftenest of a rounded form, or looking like pieces of what was
originally round, and usually wholly or partly covered with a glaze
formed of the fused substance itself. If we slowly heat a lump of loaf
sugar all through, it will form a pasty mass, while we may also hold it
without inconvenience in our fingers to the gas-flame a few seconds,
when it will be melted only on the side next the sudden heat, and
rounded by the melting. The sharp contrast of the melted and the rough
side is something like that of the meteorites; and just as the sugar
does not burn the hand, though close to where it is brought suddenly
to a melting heat, a mass of ironstone may be suddenly heated on the
surface, while it remains cold on the inside. But, however it got
there, the stone undoubtedly comes from the intensely cold spaces above
the upper air; and what is the source of such a heat that it is melted
in the cold air, and in a few seconds?
[Illustration: FIG. 79.--METEORS OBSERVED NOV. 13 AND 14, 1868, BETWEEN
MIDNIGHT AND FIVE O’CLOCK, A. M.]
Everybody has noticed that if we move a fan gently, the air parts
before it with little effort, while, when we try to fan violently,
the same air is felt to react; yet if we go on to say that if the
motion is still more violent the atmosphere will resist like a solid,
against which the fan, if made of iron, would break in pieces, this may
seem to some an unexpected property of the “nimble” air through which
we move daily. Yet this is the case; and if the motion is only so quick
that the air cannot get out of the way, a body hurled against it will
rise in temperature like a shot striking an armor-plate. It is all a
question of speed, and that of the meteorite is known to be immense.
One has been seen to fly over this country from the Mississippi to
the Atlantic in an inappreciably short time, probably in less than
two minutes; and though at a presumable height of over fifty miles,
the velocity with which it shot by gave every one the impression that
it went just above his head, and some witnesses of the unexpected
apparition looked the next day to see if it had struck their chimneys.
The heat developed by arrested motion in the case of a mass of iron
moving twenty miles a second can be calculated, and is found to be
much more than enough, not only to melt it, but to turn it into vapor;
though what probably does happen is, according to Professor Newton,
that the melted surface-portions are wiped away by the pressure of the
air and volatilized to form the luminous train, the interior remaining
cold, until the difference of temperature causes a fracture, when the
stone breaks and pieces fall,--some of them at red-hot heat, some of
them possibly at the temperature of outer space, or far below that of
freezing mercury.
Where do these stones come from? What made them? The answer is not yet
complete; but if a part of the riddle is already yielding to patience,
it is worthy of note, as an instance of the connection of the sciences,
that the first help to the solution of this astronomical enigma came
from the chemists and the geologists.
The earliest step in the study, which has now been going on for many
years, was to analyze the meteorite, and the first result was that it
contained no elements not found on this planet. The next was that,
though none of these elements were unknown, they were not combined
as we see them in the minerals we dig from the earth. Next it was
found that the combinations, if unfamiliar at the earth’s surface and
nowhere reproduced exactly, were at least very like such as existed
down beneath it, in lower strata, as far as we can judge by specimens
of the earth’s interior cast up from volcanoes. Later, a resemblance
was recognized in the elements of the meteorites to those found by the
spectroscope in shooting stars, though the spectroscopic observation
of the latter is too difficult to have even yet proceeded very far.
And now, within the last few years, we seem to be coming near to a
surprising solution.
It has now been shown that meteoric stones sometimes contain pieces
of essentially different rocks fused together, and pieces of
detritus,--the wearing down of older rocks. Thus, as we know that
sandstone is made of compacted sand, and sand itself was in some
still earlier time part of rocks worn down by friction,--when it is
shown, as it has been by M. Meunier, that a sandstone penetrated by
metallic threads (like some of our terrestrial formations) has come
to us in a meteorite, the conclusion that these stones may be part
of some old world is one that, however startling, we cannot refuse
at least to consider. According to this view, there may have been a
considerable planet near the earth, which, having reached the last
stage of planetary existence shown in the case of our present moon,
went one step further,--went, that is, out of existence altogether, by
literal breaking up and final disappearance. We have seen the actual
moon scarred and torn in every direction, and are asked to admit the
possibility that a continuance of the process on a similar body has
broken it up into the fragments that come to us. We do not say that
this is the case, but that (as regards the origin of some of the
meteorites at least) we cannot at present disprove it. We may, at any
rate, present to the novelist seeking a new _motif_ that of a meteorite
bringing to us the story of a lost race, in some fragment of art or
architecture of its lost world!
We are not driven to this world-shattering hypothesis by the absence
of others, for we may admit these to be fragments of a larger body
without necessarily concluding that it was a world like ours, or, even
if it were, that the world which sent them to us is destroyed. In view
of what we have been learning of the tremendous explosive forces we
see in action on the sun and probably on other planets, and even in
terrestrial volcanoes to-day, it is certainly conceivable that some
of these stones may have been ejected by some such process from any
sun, or star, or world we see. The reader is already prepared for
the suggestion that part of them may be the product of terrestrial
volcanoes in early epochs, when our planet was yet glowing sunlike with
its proper heat, and the forces of Nature were more active; and that
these errant children of mother earth’s youth, after circulating in
lengthened orbits, are coming back to her in her age.
Do not let us, however, forget that these are mostly speculations only,
and perhaps the part of wisdom is not to speculate at all till we learn
more facts; but are not the facts themselves as extraordinary as any
invention of fancy?
Although it is true that the existence of the connection between
shooting stars and meteorites lacks some links in the chain of proof,
we may very safely consider them together; and if we wish to know what
the New Astronomy has done for us in this field, we should take up
some treatise on astronomy of the last century. We turn in one to the
subject of falling stars, and find that “this species of Star is only
a light Exhalation, almost wholly sulphurous, which is inflamed in
the free Air much after the same manner as Thunder in a Cloud by the
blowing of the Winds.” That the present opinion is different, we shall
shortly notice.
All of us have seen shooting stars, and they are indeed something
probably as old as this world, and have left their record in mythology
as well as in history. According to Moslem tradition, the evil genii
are accustomed to fly at night up to the confines of heaven in order to
overhear the conversation of the angels, and the shooting stars are the
fiery arrows hurled by the latter at their lurking foes, with so good
an aim that we are told that for every falling star we may be sure that
there is one spirit of evil the less in the world. The scientific view
of them, however, if not so consolatory, is perhaps more instructive,
and we shall here give most attention to the latter.
To begin with, there have been observed in history certain times when
shooting stars were unusually numerous. The night when King Ibrahim Ben
Ahmed died, in October, 902, was noted by the Arabians as remarkable in
this way; and it has frequently been observed since, that, though we
can always see some of these meteors nightly, there are at intervals
very special displays of them. The most notable modern one was on
Nov. 13, 1833, and this was visible over much of the North American
continent, forming a spectacle of terrifying grandeur. An eyewitness in
South Carolina wrote:--
“I was suddenly awakened by the most distressing cries that ever
fell on my ears. Shrieks of horror and cries for mercy I could
hear from most of the negroes of the three plantations, amounting
in all to about six hundred or eight hundred. While earnestly
listening for the cause I heard a faint voice near the door,
calling my name. I arose, and, taking my sword, stood at the
door. At this moment I heard the same voice still beseeching me
to rise, and saying, ‘O my God, the world is on fire!’ I then
opened the door, and it is difficult to say which excited me
the most--the awfulness of the scene, or the distressed cries
of the negroes. Upwards of one hundred lay prostrate on the
ground,--some speechless and some with the bitterest cries, but
with their hands raised, imploring God to save the world and
them. ‘The scene was truly awful; for never did rain fall much
thicker than the meteors fell toward the earth; east, west,
north, and south, it was the same.”
The illustration on page 189 does not exaggerate the number of the
fiery flashes at such a time, though the zigzag course which is
observed in some is hardly so common as it here appears.
When it was noted that the same date, November 13th, had been
distinguished by star-showers in 1831 and 1832, and that the great
shower observed by Humboldt in 1799 was on this day, the phenomenon was
traced back and found to present itself about every thirty-three years,
the tendency being to a little delay on each return; so that Professor
Newton and others have found it possible with this clew to discover
in early Arabic and other mediæval chronicles, and in later writers,
descriptions which, fitted together, make a tolerably continuous record
of this thirty-three-year shower, beginning with that of King Ibrahim
already alluded to. The shower appeared again in November, 1867 and
1868, with less display, but with sufficient brilliance to make the
writer well remember the watch through the night, and the count of the
flying stars, his most lively recollection being of their occasional
colors, which in exceptional cases ranged from full crimson to a vivid
green. The count on this night was very great, but the number which
enter the earth’s atmosphere even ordinarily is most surprising; for,
though any single observer may note only a few in his own horizon,
yet, taking the world over, at least ten millions appear every night,
and on these special occasions very many more. This November shower
comes always from a particular quarter of the sky, that occupied by the
constellation Leo, but there are others, such as that of August 10th
(which is annual), in which the “stars” seem to be shot at us from the
constellation Perseus; and each of the numerous groups of star-showers
is now known by the name of the constellation whence it seems to come,
so that we have _Perseids_ on August 10th, _Geminids_ on December 12th,
_Lyrids_, April 20th, and so on.
The great November shower, which is coming once more in this century,
and which every reader may hope to see toward 1899, is of particular
interest to us as the first whose movements were subjected to analysis;
for it has been shown by the labors of Professor Newton, of Yale, and
Adams, of Cambridge, that these shooting stars are bodies moving around
the sun in an orbit which is completed in about thirty-three years. It
is quite certain, too, that they are not exhalations from the earth’s
atmosphere, but little solids, invisible till they shine out by the
light produced by their own fusion. Each, then, moves on its own track,
but the general direction of all the tracks concurs; and though some
of them may conceivably be solidified gases, we should think of them
not as gaseous in form, but as solid shot, of the average size of
something like a cherry, or perhaps even of a cherry-stone, yet each
an independent planetoid, flying with a hundred times the speed of a
rifle-bullet on its separate way as far out as the orbit of Uranus;
coming back three times in a century to about the earth’s distance from
the sun, and repeating this march forever, unless it happen to strike
the atmosphere of the earth itself, when there comes a sudden flash of
fire from the contact, and the distinct existence of the little body,
which may have lasted for hundreds of thousands of years, is ended in a
second.
If the reader will admit so rough a simile, we may compare such a
flight of these bodies to a thin swarm of swift-flying birds--thin, but
yet immensely long, so as to be, in spite of the rapid motion, several
years in passing a given point, and whose line of flight is cut across
by us on the 13th of November, when the earth passes through it. We
are only there on that day, and can only see it then; but the swarm is
years in all getting by, and so we may pass into successive portions
of it on the anniversary of the same day for years to come. The stars
appear to shoot from Leo, only because that constellation is in the
line of their flight when we look up to it, just as an interminable
train of parallel flying birds would appear to come from some definite
point on the horizon.
We can often see the flashes of meteors at over a hundred miles, and
though at times they may seem to come thick as Hakes of falling snow,
it is probable, according to Professor Newton, that even in a “shower”
each tiny planetoid is more than ten miles from its nearest neighbor,
while on the average it is reckoned that we may consider that each
little body, though possibly no larger than a pea, is over two hundred
miles from its neighbor, or that to each such grain there is nearly
ten million cubic miles of void space. Their velocity as compounded
with that of the earth is enormous, sometimes forty to fifty miles per
second (according to a recent but unproved theory of Mr. Denning, it
would be much greater), and it is this enormous rate of progress that
affords the semblance of an abundant fall of rain, notwithstanding the
distance at which one drop follows another. It is only from their light
that we are able to form a rough estimate of their average size, which
is, as we have seen, extremely small; but, from their great number,
the total weight they add to the earth daily may possibly be a hundred
tons, probably not very much more. As they are as a rule entirely
dissipated in the upper air, often at a height of from fifty to seventy
miles, it follows that many tons of the finest pulverized and gaseous
matter are shot into the earth’s atmosphere every twenty-four hours
from outer space, so that here is an independent and constant supply
of dust, which we may expect to find coming down from far above the
highest clouds.
Now, when the reader sees the flash of a shooting star, he may, if he
please, think of the way the imagination of the East accounts for it,
or he may look at what science has given him instead. In the latter
case he will know that a light which flashed and faded almost together
came from some strange little entity which had been traversing cold
and vacant space for untold years, to perish in a moment of more than
fiery heat; an enigma whose whole secret is unknown, but of which,
during that instant flash, the spectroscope caught a part, and found
evidence of the identity of some of its constituents with those of the
observer’s own body.
VII.
COMETS.