It was Edmund Halley who first revealed a source of danger from Comets,
of which even medieval superstition had never dreamed.
While he was patiently plotting out the orbit of the Comet of 1680,
which had inspired no little dismay among his contemporaries, Halley
found that the Earth’s orbit had been approached by the Comet within
four thousand miles—half the diameter of the Earth.
If the Earth had been struck by that fiery wanderer?
None had ever thought of the possibility.
Halley began to do some mathematical figuring, and decided that, if a
Comet’s mass were comparable with that of the Earth, our year would
have been changed in length because the Earth’s orbit would have been
altered. He also speculated what would happen to the Earth, and reached
this conclusion:
“If so large a body with so rapid a motion were to
strike the Earth—a thing by no means impossible—the
shock might reduce this beautiful world to its
original chaos.”
Halley even thought it probable that the Earth had actually been struck
by a Comet at some remote period, struck obliquely, moreover, so that
the axis of rotation had been changed. Thus he was led to infer that
possibly the North Pole had once been at a point near Hudson’s Bay, and
that the rigour of North America’s climate might thus be accounted for.
The seed which was thus sown by Halley has borne fruit. In Halley’s
own time, learned men were brooding over the ultimate destruction of
the Earth by collision with a Comet.
Dr. Whiston, who succeeded Newton at Cambridge in the Lucasian chair of
mathematics, was sure that a Comet caused the Deluge, and went so far
as to prophesy that a Comet, as it passed us on its outward course from
the Sun, would ultimately bring about a “General Conflagration,” and
thus envelope the Earth in flames.
One century after Halley, the French astronomer Laplace, whose
mathematical attainments were surpassed only by those of Newton,
applied his brilliant mind to the possibility of a collision with a
Comet, and arrived at this conclusion:
“The seas would abandon their ancient beds and rush
towards the new equator, drowning in one universal
deluge the greater part of the human race.... We see,
then, in effect, why the ocean has receded from the
high lands upon which we find incontestable marks of
its sojourn; we see how the animals and plants of the
south have been able to exist in the climate of the
north, where their remains and imprints have been
discovered.”
The famous French mathematician Lalande showed that if a Comet as heavy
as the Earth were to come within six times the distance of the Moon,
it would exert such a powerful attraction upon the waters of the globe
as to pull up a tidal wave 13,000 feet above the ordinary sea-level
and inundate the continents Every European mountain would be submerged
except Mt. Blanc, and only the inhabitants of the Rockies, the Andes
and the Himalayas would escape death.
Since Lalande’s day there has been more than one Comet “scare.” One of
these startled Europe in 1832. On October 29th of that year, Biela’s
Comet crossed the Earth’s orbit. The announcement was received with
stupefaction. It was only when Arago soothingly pointed out that the
Earth would not reach the exact point where the Comet had intersected
the Earth’s orbit until November 30, at which time the Comet would be
50,000,000 miles away, that the popular excitement subsided. A similar
alarm seized the world in 1857. Some prophet declared that on June 13
the world would collide with a certain periodic Comet having a period
of revolution of three centuries. It is related that the churches
and confessionals were crowded for days. Still another prediction,
made in 1872 by Plantamour, the distinguished director of the Geneva
Observatory, set Europe in a ferment. His calculations were based on
errors, which were pointed out by other astronomers, and the public
mind was quieted.
Although more than two centuries have passed since Halley was in his
prime, the possibility of a collision with some vagabond star still
haunts the mind of the astronomer.
That a collision is apt to occur is an admitted astronomic fact. The
latest estimate, made in 1909 by Prof. William H. Pickering of Harvard
University, would seem to prove that the core of one Comet in about
100,000,000 Comets will hit the earth squarely. An encounter with some
part of a Comet’s head will happen once in 4,000,000 years. Since
Comets’ orbit are more thickly distributed near the ecliptic than else
where in the celestial sphere, the collisions will occur according to
Pickering, perhaps more frequently than this.
Because Pickering’s figures differ from those other astronomers—Arago
and Babinet, for instance—it must not be inferred that his
predecessors are wrong and that he is right in his calculations. The
problem is too complex for that. Pickering, Arago and Babinet differ
partly because they have assumed different average sizes for their
Comets, and partly because their definitions of visible Comets are not
in accord.
That the possibility is very real, we shall all have an opportunity of
judging on May 18, 1910. On that date the Earth will be plunged in the
tail of Halley’s Comet, and the head will be less than 15,000,000 miles
away—a mere hand’s breadth in the vastness of the universe.
What will happen?
Nobody knows for certain.
By means of the wonderful instrument called the spectroscope, an
instrument which analyzes a distant star as readily as if it were a
stone picked up in the road, it has been discovered that a Comet’s tail
is composed of gases called “hydrocarbons” (combinations of hydrogen
and carbon), and that it bears a close chemical resemblance to the blue
flame of a kitchen gas-stove.
Illuminating gas, as we all know, is poisonous. If a Comet’s tail were
dense enough, it is conceivable, therefore, that every human being on
this planet might be asphyxiated by breathing the Comet’s poisonous
vapour as the Earth plowed through it. There is also this possibility,
suggested by Flammarion, that the gases of a very dense tail might so
combine with the nitrogen which constitutes nearly 80 per cent. of
the air we breathe, that the atmosphere would be converted into the
“laughing gas” employed by dentists. The world would die in a delirium
of joy. At first a delightful serenity would settle upon mankind. Then
would follow a contagious gaiety, febrile exaltation, a paroxysm of
delight, and then madness. Flammarion even conceives the world merrily
dancing a joyous, hysterical sarabande in which it perishes laughing.
The tail of a Comet is fraught with still other possible dangers. Our
atmosphere contains a certain amount of hydrogen, a marvellously light
gas to which balloons owe their buoyancy. Besides its lightness, this
gas is characterized by an extreme inflammability. The law of the
diffusion of gases teaches us that part of this hydrogen in the air
is mechanically mixed with other gases, and that part of it probably
floats in the upper air, far beyond the reach of any balloon. A Comet
may be regarded as a huge lighted torch whirling through space, which
may be brought dangerously near that upper layer of highly inflammable
hydrogen. If the gas shall ever be touched off by this flying torch,
our planet will be ignited. The whole atmosphere will become a seething
ocean of flame, in which forests and cities will burn like straw, in
which oceans will boil away in vast clouds of steam, and in which all
animal life will be snuffed out of existence before it shall realize
that the world is on fire. In a word, the globe will become a planetary
funeral pyre. Since water results from burning hydrogen in oxygen,
this same fierce and terrible flame must be speedily extinguished by a
mighty deluge which will engulf the Earth.
A spectroscope analysis of Halley’s Comet has furthermore revealed
the presence of cyanogen gas in the tail. Cyanogen is a compound of
nitrogen and carbon, one of the most poisonous compounds with which the
chemist is familiar. Prussic acid, potassium cyanide and many other
cyanides, all of them almost instantaneously fatal if taken into the
human system, are compounds of cyanogen. If that gas is present in
large enough quantities, one flick of a Comet’s tail will end all human
and animal existence.
So much is certain. A collision of the Earth with a Comet will
undoubtedly prove disastrous—how disastrous will depend largely on the
size of the Comet’s head and on its speed. That a violent heat will
be developed, we have every reason to believe, from our knowledge of
meteors. The mere movement of a meteor through the thin upper layers of
our atmosphere produces a dazzling trail and reduces the meteor itself
to a molten metallic mass. Arrest a body in swift motion, and you must
dissipate its energy in some way. As a rule, the energy is converted
into heat. A bullet discharged from a rifle is often melted when
suddenly stopped by steel armour. A Comet travels at a pace compared
with which a projectile, fired from the most powerful twelve-inch gun,
seems only to crawl. What, then, must be the frightful effect when it
strikes the Earth?
A Comet rushes through space not at the bullet’s rate of thousands of
feet an hour, but of a million miles an hour. The bigger it is, and the
faster it moves, the greater will be the heat developed by its stoppage.
“At the first contact with the upper regions of the atmosphere,” writes
Prof. Simon Newcomb, “the whole heavens would be illuminated with a
resplendence beyond that of a thousand Suns, the sky radiating a light
which would blind every eye that beheld it, and a heat which would melt
the hardest rocks.” The same conclusion was reached by Prof. Faye.
When the time comes for a collision with a Comet of formidable size,
the human race will be in the horrible predicament of knowing the exact
hour and minute of its doom. The newspapers will print a dispatch from
some great observatory, reading perhaps like this:
“A telescopic Comet was discovered by Caxton in right ascension 7 hours
13 minutes 1 second, and declension 17 degrees 28 minutes 31 seconds.
Moderate motion in a northwest direction.”
[Illustration: “If so large a body with so rapid a motion were to
strike the Earth—a thing by no means impossible—the shock would
reduce this beautiful world to its original chaos.”—EDMUND HALLEY.]
At first the discovery produces not even a ripple of excitement.
Telescopic Comets are discovered too frequently. Three days later the
discoverer has worked out an ephemeris, which gives the date when the
body will pass around the Sun, and which indicates the Comet’s path. He
finds that on a certain date and at a certain hour the Earth and the
Comet must crash together. Again and again he repeats his calculations,
hoping that he may have erred. The utmost permissible allowance for
accelerations and retardations caused by the outer planets of the solar
system fails to change the result.
The Earth and the Comet must meet. With some hesitation the astronomer
sends a telegram to a central observatory, which acts as a distributor
of astronomical news. At first his prediction is discredited and even
laughed at. Another computation is made at the observatory. Again
mathematics infallibly indicates the exact time and place of the
encounter, and the last lingering hope is dispelled. Telegrams are sent
to astronomical societies, to the leading scientific periodicals and to
the newspapers.
At first the prediction of the Earth’s doom is received with popular
incredulity, engendered by years of newspaper misrepresentation. The
world’s end has been too frequently and too frightfully foretold
on flamboyant double-page Sunday editions. When the truth is at
last accepted, after days of insistent repetition of the original
announcement, a wave of terror runs through the world.
There is no escape. International committees of astronomers meet
daily to mark the approach of the Comet. Bulletins are published
announcing the steadily dwindling distance between the world and the
huge projectile in the sky. The great tail, arching the Heavens as the
Comet approaches, seems like a mighty, fiery sword held in an unseen
Titanic hand and relentlessly sweeping down. The temples, churches and
synagogues are thronged with supplicating multitudes on bended knees,
in a catalepsy of terror. The stock exchanges, banks, shops and public
institutions are deserted. Business is at a standstill. The roar of the
street is hushed. No wagons rattle over the pavement; no hucksters call
out their wares.
As the Comet draws nearer and nearer, night changes into an awful,
nocturnal day. Even at noon the Comet outshines the Sun. There is no
twilight. The Sun sets; but the Comet glows in the sky, another more
brilliant luminary, marvellously yet fearfully arrayed in a fiery plume
that overspreads the sky. The Moon is completely lost, and the Stars
are drowned out in this dazzling glare. Warned by the astronomers,
mankind takes refuge in subterranean retreats to await its fate.
Long before the actual collision—long before the Earth is reduced
to a maelstrom of lava, gas, steam and planetary debris—mankind is
annihilated with merciful swiftness by heat and suffocation. A candle
flame blown out by a gust of wind is not more quickly extinguished.
When the Comet encounters the upper layers of the atmosphere, there is
a blinding flash, due to friction between the air and the Comet. A few
seconds later the crash comes. From within, molten rock and flame, pent
up for geologic ages, burst forth, geyser-like. The Earth is converted
into a gigantic volcano, in the eruption of which oceans are spilled
and continents are torn asunder, to vanish like wax in a furnace.
When it is all over, the Earth swims through space, a blackened
planetary cinder,—desolate and dead.