Chapter III: Part 3

All through the year 1758 the most noted astronomers of Europe were on the lookout for the return of the predicted Comet. One of these astronomers, Messier, looked for it through his telescope at the Paris Observatory every night from sunset to sunrise throughout that whole year. On Christmas night, 1758, the Comet was first seen by a German peasant near Dresden, who had heard about the Comet and was looking for it. He was a man of unusually good eyesight, yet his discovery was doubted until Messier, nearly a month afterward, at Paris, “picked up” the Comet with his telescope.

From that time forth this Comet, which returned in 1835, and is reappearing in this year (1910), has been known as Halley’s Comet.

Besides this achievement, Halley accomplished many other noteworthy feats in astronomy, such as his discovery of the proper motions of the fixed stars; his detection of the “long inequality” of Jupiter and Saturn, and of the acceleration of the moon’s mean motion; his theory of variation, including the hypothesis of various magnetic poles, with his suggestion of the magnetic origin of the aurora borealis; and his indication of a method still used for determining the solar parallax by means of the transits of Venus.

On the strength of these achievements, Halley for many years was elected to serve as secretary to the Royal Society. Commissioned as a Captain in the Royal Navy, he also commanded a vessel on a long cruise of exploration, and late in life he was made Astronomer Royal.

Although in his sixty-fourth year, he then undertook to observe the moon through an entire revolution of her nodes (eighteen years), and actually carried out his purpose. To appreciate the full significance of so painstaking an achievement it should be borne in mind that astronomical observations must be made in a temperature equal to that of the open air. Observatories cannot be heated because the heat would impair the accuracy of the instruments.

Great astronomers, like poets, are born, not made. Edmund Halley was one of these. At the age of seventeen he had already observed the change in the variations of the compass. At nineteen he was recognized as an astronomer of reputation, having supplied a new and improved method of determining the elements of the planetary orbits. His detection of considerable errors in the tables then in use led him to the conclusion that a more accurate determination of the places of the fixed Stars was indispensable to the progress of astronomy. With this end in view he set out on a voyage to the other side of the globe, St. Helena, where he undertook the task of making complete new observations of the entire Southern Hemisphere. Though the Heavens proved clouded he succeeded within two years in registering three hundred and sixty stars, a colossal achievement which won for him the title of the “Southern Tycho.” This was when Halley was barely of age.

(The famous astronomer Tycho Brahe, long before this had won his fame by mapping the stars of the Northern Heavens.)

No one could well have begun with prospects more remote from so high a career, for Edmund Halley was born in 1656, the son of a soap boiler in a shabby London suburb. From the refuse of rancid fat and lye the boy was rescued by friends, who procured for him a scholarship at Saint Paul’s school. By his brilliant attainments in mathematics he won another scholarship to Oxford University.

While at Oxford the youth published a treatise on the planetary orbits and argued the Sun’s axial rotation.

On his graduation from Oxford, the young would-be astronomer conceived the project of turning his attention to the southern Stars, of which no good observations had been made. Shortly before this time a Dutch astronomer, named Houtman, had observed these Stars in the island of Sumatra; and Blaeu, the best globe maker of the age, had used these new observations in the correction of his celestial globes. Halley, on examining these corrections, came to the conclusion that he himself could do better. He also concluded that the Island of St. Helena might be a better point for southern observations. His father, unable to pay the expenses of so long a trip, broached the project to some friends. The young astronomer was recommended to King Charles II. by Williamson and Jones Moore, and the King in turn recommended the youth to the Indian Company, which then had control over the island of St. Helena.

After this all was plain sailing. The India Company placed a ship at his disposition and promised him all the assistance he required. Young Halley provided himself with telescopes, and micrometers, and other instruments of the latest approved pattern. In November, 1666, at the age of twenty, he sailed for St. Helena. Among his luggage was a sextant of five and a half feet and a telescope twenty-four feet in length constructed under the supervision of Flamsteed, the Astronomer Royal.

Halley was disappointed in the climate of St. Helena. Frequent rains and a constantly hazy sky scarcely permitted any observations in the months of August and September. Notwithstanding these difficulties, he succeeded in observing and cataloguing some 360 Stars.

In addition to his work on the Stars, Halley made some investigations on the Moon’s parallax, combining his observations at St. Helena with those made in northern skies. He also evolved a new theory of the Moon’s motion, which proved of great aid in the determination of longitudes.

On November 7, 1677, Halley observed a transit of Mercury which suggested to him the important idea of employing similar phenomena for the calculation of the Sun’s distance.

Halley returned to England in November, 1678, and was hailed by his fellow astronomers as the “Southern Tycho.” He was elected a fellow of the Royal Society, and by the King’s command the degree of Master of Arts was conferred upon him by the University of Oxford.

Six months later Halley set out for Dantsic for a personal conference with Hevelius, the Polish astronomer. Halley wanted to satisfy himself as to the accuracy of observations claimed by Hevelius without the aid of a telescope. Halley convinced himself that the errors of the observations made by Hevelius were less than had been supposed, and did not exceed a minute of an arc. The two became life-long friends. Halley proceeded to other cities of Europe where there were observatories. In Paris he observed with Cassini the great Comet of 1680. This was the beginning of Halley’s special study of Comets.

Returning to England, the young astronomer married the daughter of Mr. Tooke, auditor of the Exchequer, with whom he lived harmoniously until her death, fifty-five years later. The young couple settled at Islington, where Halley erected an observatory of his own and engaged in constant lunar observations with a view toward finding a method for computing longitudes at sea.

Halley’s mind at the same time was busy with the momentous problem of gravity, upon which Isaac Newton was working then. Independently of Newton, Halley reached the conclusion that the central force of the Solar System must decrease inversely as the square of the distance. Having applied vainly to his fellow astronomers, Hooke and Wren, Halley in August, 1684, made a special journey to Cambridge to consult Isaac Newton, who confirmed his conjectures.

Halley and Newton became life-long friends. Halley had Newton elected to the Royal Society, and when Newton became too poor to pay his quarterly dues, Halley, through his influence with the leading members of the Society, had them remitted. It was Halley who encouraged Newton to put his momentous discovery and elucidation of the forces of gravity into permanent form in his “Principia,” the first volume of which, “De Motu,” was presented to the Royal Society at Halley’s suggestion.

In the proceedings of the Royal Society for December, 1684, there is an entry that “Mr. Halley had lately seen Mr. Newton at Cambridge, who had told him of a curious treatise ‘De Motu,’ which at Mr. Halley’s desire he promised to send to the Society to be entered upon their register. Mr. Halley was desired to put Mr. Newton in mind of his promise for the securing this invention to himself, till such time as he could be at leisure to publish it.”

Early in the following year Newton sent his treatise to the Society, to whom it was read aloud by Halley. This treatise “De Motu” was the germ of the “Principia” and was intended to be a short account of what the greater work was to embrace.

During the next two years Newton was hard at work on his “Principia,” while Halley was equally hard at work on his computations of the Comet of 1682, and on his theory of the orbits and the periodical returns of Comets which grew out of his observations.

On April 21, 1686, Halley read to the Royal Society his own “Discourse Concerning Gravity and its Properties,” in which he stated that his “worthy countryman, Mr. Issac Newton, has an incomparable treatise on Motion almost ready for the press,” and that the law of the inverse square “is the principle on which Mr. Newton has made out all the phenomena of the celestial motions so easily and naturally that its truth is past dispute.”

Shortly afterward Newton sent in the manuscript of his great work. The Society voted “that a letter of thanks be written to Mr. Newton and that the printing of his book be referred to the consideration of the council and that in the meantime the book be put into the hands of Mr. Halley.”

The truth was that the Royal Society, at that time, did not have money enough to print the book. The Society went through the empty form of “ordering” that the book be printed “forthwith,” but no printer was forthcoming until Halley himself undertook the publication of the great work at his own expense.

The delicacy of Halley’s feeling is revealed by his correspondence with Newton, in which he informed Newton that the book had “been ordered to be printed at the Society’s charge.” The preliminary delay about printing he explained to Newton “arose from the President’s attendance on the King, and the absence of the vice-presidents, whom the good weather had drawn out of town.”

Later Newton came to realize how much he owed to Halley in this matter. In his letters to Halley henceforth he always referred to his book as if it had been Halley’s book. When the great work was finished at last Newton wrote to Halley under the date of July 5, 1687: “I have at length brought your book to an end, and hope it will please you.”

The finished work contained a note to this effect: “The inverse law of gravity holds in all the celestial motions, as was discovered also independently by my countrymen Wren, Hooke, and Halley.”

The book was dedicated to the Royal Society, and to it was prefixed a set of Latin hexameters addressed by Halley to the author, ending with the well known line:

“Nec fac est propius mortali attingere divos.”

(“It is not given to a mortal to get in closer touch
with the gods.”)

Halley was fifty years old when he made his famous prediction of the return of the Comet of 1682. This was in his “Synopsis of Comet Astronomy,” which ended with these words: “Hence I may venture to foretell that this Comet will return again in the year 1758.”

Besides being an astronomer of the first class, Halley was also a good navigator. In 1698 he was commissioned a captain in the Royal Navy and was put in command of the King’s ship, “The Paramour Pink.” With this vessel he set out on a long cruise to the Pacific for the purpose of making observations on the laws which govern magnetic variations. This task he accomplished in a voyage which lasted two years and extended to the fifty-second degree of southern latitude, when the ice compelled him to turn back. On the return voyage his crew mutinied and his lieutenant sided with the mutineers. Halley quelled the mutiny by sheer force of personality, and returning to England got rid of his lieutenant. The results of his voyage were published in his “General Chart of the Variation of the Compass” in 1701. Immediately afterwards Halley set out on another King’s ship and executed by royal command a careful survey of the tides and coasts of the British Channel, an elaborate chart of which he published in 1702.

Next Halley was sent by the King to Dalmatia, for the purpose of selecting and fortifying the port of Trieste.

On Halley’s return to England, he was made Savilian professor of geometry at Oxford, and received an honorary doctor’s degree. He filled two terms of eight years each as secretary to the Royal Society, and early in 1720 he succeeded Flamsteed as Astronomer Royal.

He died on January 14, 1742, at the age of eighty-five in the full possession of his faculties, the foremost astronomer of the day and a man universally beloved and respected. His gravestone stands at the Greenwich Observatory.

Halley’s works fill several shelves in the library of the Royal Society. His fame is kept green by the periodical return of the wandering star known by his name.

WHAT ARE COMETS?

The modern answer to the question “What are Comets made of?” is this:

Probably the heads are a mixture of solid and gaseous matter. The tails are gaseous—the result of the volatilisation of the solid matter of the heads.

The spectroscope shows that gases appear to be a constituent of all Comets. The spectra of Comets are very similar to those of a Bunsen flame. Recent spectroscopic photographs have revealed the presence of hydrocarbons, nitro-carbons, of cyanogen and of the vapours of sodium, iron and other metals.

The connection between Comets and Meteors implies the presence in Comets of solid matter. A modern theory, voiced by Schiaparelli, is that meteor showers are broken up Comets.

The tails of Comets appear to be composed of luminous gases ejected from the head of the Comet through a solar force held to be “Light Pressure,” which causes these tails to shoot off and disperse into space at the rate of 865,000 miles an hour.

The length of some Comets’ tails has been estimated at 125,000,000 miles, while the Comets’ heads themselves are generally much larger in size than our Earth. Halley’s Comet is more than ten-fold the size of our Earth.

E. W. Maunder, of the Royal Observatory of Greenwich, a modern astronomer, has thus summarized the latest theories of the substance of Comets:

“Though the bulk of comets is huge, they contain extraordinarily little substance. Their heads must contain some solid matter, but it is probably in the form of a loose aggregation of stones enveloped in vaporous material. There is some reason to suppose that Comets are apt to shed some of these stones as they travel along their paths, for the orbits of the meteors that cause some of our greatest ‘star showers’ are coincident with the paths of Comets that have been observed. But it is not only by shedding its loose stones that a Comet diminishes its bulk; it loses also through its tail. As the Comet gets close to the Sun its head becomes heated, and throws off concentric envelopes, much of which consists of matter in an extremely fine station of division.”

The orbits of Comets visible to human eyes are all governed by the Sun. In the words of C. L. Poor: “The attraction of the Sun is to the Comet like the flame to the moth. The Comet flutters for a moment about the Sun, and then swings back into outward space. But not unscathed; like the moth, the Comet has been singed. The fierce light of the Sun has beaten upon it, and spread out its particles and scattered them along its path.”

As a comet swings toward and away from the Sun, it travels at a tremendous rate of speed—over a million miles an hour. The distance covered from one end of the orbit to the other is 3,370,000,000 miles.

The great majority of Comets appear to travel in parabolas, open curves leading from infinite space to and around the Sun, and thence back into infinite space to some other fixed star invisible to us. As a matter of fact, though, the parabolic curves of Comets’ orbits through the gravitational attraction of the planets, whose orbits are crossed by it, may be changed into hyperbolic curves and ellipses by planetary perturbations. Hence the differences in time between the returns of certain Comets, like Halley’s, for instance.

In a general way, it may be said that every Comet comprises a nucleus, an envelope (called the “coma”) surrounding the nucleus and measuring from 20,000 to 1,000,000 miles in diameter, and a long tail which streams behind the nucleus from sixty to a hundred million miles or more.

Astronomers have decided that the nucleus is probably a heap of meteorites varying in size from a grain to masses weighing several tons each; a heap, moreover, so easily sundered that its elements are distributed gradually along the orbit. It follows that every Comet must eventually perish unless it restores its nucleus by collecting stray meteors. That disintegration does occur has been observed time and time again.

For example, Biela’s Comet, which was discovered in 1826, burst into two fragments, which drifted apart a distance of one million miles. Thus it became a twin Comet. Eventually it disappeared as a Comet, and in its stead we see a shoal of meteors whenever we cross its track every six and a half years.

It is possible that the Comets of 1668, 1843, 1880, 1882 and 1887, all travelling in approximately the same path, are fragments of a single large body which was broken up by the gravitational action of other bodies in the system, or through violent encounter with the Sun’s surroundings.

The luminous tail which streams behind the nucleus, which Shakespeare described so beautifully as “crystal tresses,” is startling, to say the least. Despite a length which may exceed a hundred million miles, it is so diaphanously light and subtle that it is difficult to compare it with any earthly fabric. The air that we breathe is a dense blanket in comparison. Several hundred cubic miles of the matter composing that wonderful luminous plume would not outweigh a jarful of air. By reason of its fairy lightness, it is possible for a tail occupying a volume thousands of times greater than the sun to sweep through our solar system without causing any perturbations in planetary movements.

No celestial phenomenon has caused more perplexity than the ghostly sheaf of light we call a Comet’s tail. In a day, in a few hours even, the form of that wonderful gossamer may change. Hence it is that periodic Comets are identified when they return, not by the length and arch of their tails, but by their orbits. These alone are permanent.

When a Comet is first seen in the telescope, it appears as a diminutive filmy patch, often unadorned by any tail. As it travels on toward the Sun, at a speed compared with which a modern rifle bullet would seem to crawl, violent eruptions occur in the nucleus.

The ejected matter is bent back to form the cloak called the “coma.” With a nearer approach to the sun, the tail begins to sprout, increasing in size and brightness as it proceeds. Evidently there is some connection between the Sun and the tail, something akin to cause and effect.

When the Comet rushes on toward the Sun, invariably the tail drifts behind the nucleus like the smoke from a locomotive. But when the Comet swings around the Sun and travels away from it, a startling change takes place. The tail no longer trails behind, but projects in front as if some mighty solar wind were blowing it in advance of the head.

This phenomenon has long been an astronomical riddle. Here was a kind of matter that refused to obey the laws of gravitation and yield to the enormous pull of the Sun.

It was thought for a time that the tail was flung away from the Sun by stupendous repelling electrical forces. That electricity plays its part in the formation of the fairy plume is conceivable, and even probable; but recently the physicist has discovered a new source of repellent energy which very plausibly explains the mystery of a Comet’s tail.

This new source of energy is nothing less than the pressure or push of the Sun’s light. Solar gravitation is a force more powerful than we can realize. If it were possible for us to live on the Sun, we would find ourselves pulled down so violently that our body would weigh two tons. Our clothing alone would weigh more than one hundred pounds. Running would be a very difficult athletic feat. Light-pressure must indeed be powerful if it can conquer so relentless a force.

Because we have never seen objects torn from our hands by the pressure of light, it may be inferred that this newly discovered force affects only bodies that are invisibly small. With the aid of instruments that feel what our hands can never feel and see what our eyes can never see, the modern physicist has critically analyzed the radiation that beats upon the earth from the distant Sun.

Light really does sway infinitely small particles, as was first experimentally proved by the Russian Lebedev. Two American astronomers, Nichols and Hull, improved upon his method. They cast the solar effulgence into mighty mathematical scales and found that the earth sustains a light-load of no less than 75,000 tons.

Most city-bred people are familiar with the so-called “Sun Motors”—little mills with black and white wings, enclosed in airtight vessels, which spin around in “perpetual motion” under the effect of “Sun Pressure.”

It remained for the broad mind of a Swedish physicist, Svante Arrhenius, to apply the principle of light-pressure cosmically. He explained, very simply, that because a Comet’s tail is composed of a very fine dust it can easily be driven away from the Sun by radiation pressure.

To understand how it is possible for so immaterial a thing as a sunbeam to produce so huge an effect, we have only to take a very simple example.

Assume that you have before you a block of wood weighing one pound. The block exposes a certain amount of surface to the Sun’s light. Saw the block in half, and you increase the amount of that surface. Divide each half again into half, and the exposed surface is further augmented. If this process of subdivision is carried on far enough, the block will be reduced to sawdust.

The entire mass of sawdust still weighs one pound; but its surface has been vastly enlarged. Indeed, the particles of sawdust, individually considered, may be said to consist of much surface and very little weight. If it were possible to take each granule of visible sawdust and subdivide it into invisible particles, a point would be reached where the pressure of light would exactly counterbalance the pull of gravitation, so that the particles would remain suspended in space, perfectly balanced in the scale of opposing cosmic forces.

Finally, if the subdivision be continued beyond this critical point, the particles will be wrenched away from the grip of gravitation and hurled out into space by the pressure of light.

So much has been discovered about the particles that compose a Comet’s tail that the more progressive scientists of our day have accepted this ingenious theory. Thus it has been decided by them that the delicate tresses of a Comet are to a large extent composed of fine particles of dust and soot.

Before we can completely accept the view that light-pressure forms this train of soot we must ascertain whether the pressure of light is capable of accounting for the flash-like rapidity with which a Comet’s tail changes.

A Comet may throw out a tail sixty million miles long in two days. Is it actually possible for light-pressure to accomplish that astonishing feat? Arrhenius has computed that 865,000 miles an hour is the speed of a light-flung particle of one-half the critical diameter. Because they are only one-eighteenth as large as this particle of critical diameter, the dust grains in a Comet’s tail would be propelled over the same 865,000 miles in less than four minutes. It follows that the solar radiation is amply strong enough to toss out a tail of sixty million miles in two days.

Photography in the hands of Prof. E. E. Barnard, of the Yerkes Observatory, has revealed some extraordinary changes in Comets’ tails, changes which are not apparent to the eye and which cannot be explained by light-pressure or by solar electrical forces. He has collected a formidable mass of photographic evidence which seems to show that there are other influences at work besides the Sun’s radiation, and that these influences manifest themselves in distorting and breaking a Comet’s tail. In some Comets of recent years, streams of matter have been shot out in large angles to the main direction of the tail without being at all bent by the pressure of light. In Morehouse’s Comet of 1908, tails were repeatedly formed and discarded to drift bodily out into space and melt away. Sometimes the photographic plate has shown the tail twisted like a corkscrew and sometimes it has revealed masses of matter at some distance from the head, where apparently no supply had reached it. At one time the entire tail of Morehouse’s Comet was thrown violently forward, a peculiarity so utterly opposed to the laws of gravitation that Professor Barnard suspects some unknown force at work in planetary space besides a force which undoubtedly resides in the Comet itself. If Halley’s Comet serves no other purpose than to throw light upon this mystery, its return will more than repay astronomers for all their observatory vigils.

From the fact that the matter is ejected from the head to form the tail, it would follow that, unless it has the means of rejuvenating itself, a comet must eventually be disintegrated. Instances of this fragmentation and, eventual disappearance of a Comet are not wanting in astronomical annals. It has been stated previously that when Biela’s Comet appeared in 1846 it became distorted and elongated, that it eventually split up into two separate bodies, that in 1852 it again appeared in its double form, and that it has since disappeared.

In a way, Comets may be said to bleed to death. At each return of Halley’s Comet, future astronomers will find it less brilliant than it was seventy-six or seventy-seven years before. Some time there will be no Halley’s Comet left, and the most famous Comet of its kind will be reduced to a shoal of meteors varying in weight from a few ounces to several tons and faithfully pursuing the orbit which their parent traced and retraced century after century.

THE PERIL OF THE COMET

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.”

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.

THE END OF THE WORLD

Camille Flammarion, the French astronomer, in his story, “The End of the World,” gives this graphic description of the results of a collision between a Comet and our Earth:

In Paris, London, Rome, Berlin, St. Petersburg, Constantinople, New York and Chicago—in all the great capitals of the world, in all the cities, in all the villages—the frightened people wandered out of doors, as one sees ants run about when their ant-hills are disturbed. All the affairs of every-day life were forgotten.

All human projects were at a standstill. People seemed to have lost interest in all their affairs. They were in a state of demoralization—a dejection more abject even than that which is produced by sea-sickness.

All places of worship had been crowded on that memorable day when it was seen that a collision with a Comet had become inevitable.

In Paris the crowds in the churches were so great that people could no longer get near Notre Dame, the Madeleine and the other churches. Within the churches, vast congregations of worshippers were on their knees praying to God on High. The churches rang with the sounds of supplication, but no other sound was heard. The great church organs and the bells in the steeples were hushed.

In the streets, on the avenues, in the public squares, there was the same dread silence. Nothing was bought or sold. No newspapers were hawked about.

The only vehicles seen on the streets were funeral hearses carrying to the cemeteries the bodies of the first victims of the Comet. Of these there were already many. They were people who had died from fright and from heart disease.

With what anxiety everyone waited for the night!

Never, perhaps, was there a more beautiful sunset. Never a clearer sky. The sun seemed to dip into a sea of red and gold.

The huge red ball of the sun sank majestically to the horizon. But the stars did not appear. Night did not come.

To the solar day succeeded a new day, the daylight of the Comet. Its intense light resembled that of an Aurora Borealis, but more vivid, coming from a great incandescent spot, which had not been visible during the day because it was below the horizon, but which would certainly have rivalled the splendour of the Sun.

This luminous spot rose in the East almost at the same time as the full Moon. The two luminous bodies rose together, side by side. As they rose, the light of the Moon seemed to pale, but the head of the Comet increased in splendour with the disappearance of the Sun below the western horizon.

Now, after nightfall, the Comet dominated the world—a scarlet-red ball with jets of yellow and green flame which seemed to flutter like fiery wings.

To the terrified people it seemed like a giant of fire taking possession of all Heaven and Earth.

Already the outermost jets of flame had reached the Moon. From one instant to the next the flaming rays would descend upon the Earth.

All eyes were distended with horror when it was seen that the horizon was lighting up with tiny violet flames as from a vast fire.

An instant afterward, the Comet diminished in brilliancy. This was apparently because the Comet, upon touching the atmosphere of our Earth, had come within the penumbra of our planet and had lost part of its reflected light coming from the Sun. But in reality this apparent extinction was the effect of contrast. When the less dazzled eyes of the awestruck, human spectators had grown used to this new light, it appeared almost as intense as at first, but paler, more sinister and sepulchral.

Never before had the Earth been lit up with so sickly a light.

The drouth of the air became intolerable. Heat, as from a huge burning oven, came from above. A horrible stench of burning sulphur—due, no doubt, to electrified ozone—poisoned the atmosphere.

All the people then saw that their time had come. Many-thousand-throated cries rent the air. “The World is burning. We are on fire!” they cried.

All the horizon, in fact, was now lit up with flame, forming a crown of blue light. It was, indeed, as had been foreseen by scientists, the oxide of carbon igniting in the air and producing anhydrid of carbon. Clearly, too, hydrogen from the Comet combined with it.

On a sudden, as the people were gazing terrified, motionless, mute, holding their breath, and scared out of their wits, the vault of Heaven seemed to be rent asunder from the zenith to the horizon. Through the gaping breach there seemed to appear the huge red mouth of a dragon, belching forth sheaves of sputtering green flames.

The glare of the atmosphere was so fierce that those who had not already hidden themselves in the cellars of their houses, now all rushed helter-skelter to the nearest underground openings, be they subway steps, cellar doors or sewer manholes. Thousands were crushed or maimed during this mad stampede, while many others, frantic from fright and stricken with the heat, fell dead from apoplexy.

All reasoning powers seemed to have ceased. Among those cowering in dark cellars and subterranean passages below, there was nothing but silence, begot by dull resignation and stupor.

Of all this panic-stricken multitude, only the astronomers had remained at their posts in the Observatories, making unceasing observations of this great astronomic phenomenon. They were the only eye-witnesses of the impending collision.

Their calculations had been that the terrestrial globe would penetrate into the core of the Comet, as a cannon ball might into a cloud. From the first contact of the extreme atmospheric zones of the Earth and of the Comet, they had figured, the transit would last four hours and a half.

It was easy to compute, since the Comet, being about fifty times as large as the Earth, was to be pierced, not in its centre, but at one-quarter of the distance from the centre, with a velocity of 173,000 kilometers an hour.

It was about forty minutes after the first atmospheric impact with the Comet, that the heat and horrible stench of burning sulphur became so suffocating that a few more moments of this torment would put an end to all life. Even the most intrepid of astronomers withdrew into the interior of their glass-domed observatories, which they could close hermetically as they descended into the deep subterranean vaults.

The longest to stay above was a young assistant astronomer, a girl student from California, whose nerves had been steeled during the ordeal of the San Francisco earthquake. She remained long enough to witness the apparition of a huge, white-hot meteorite, precipitating itself southward with the velocity of lightning.

But it was beyond human endurance to remain longer above. It was no longer possible to breathe. To the intense heat and atmospheric drouth, destroying all vital functions, was added the poisoning of our air by the oxide of carbon.

The ears rang as from the tolling of funeral bells, and all hearts were in a flutter of feverish palpitation. And always, everywhere, there was that suffocating stench of sulphur.

Now a shower of fire fell from the glowing sky. It was raining shooting-stars and white-hot meteorites, most of which burst like bombs. The fragments of these, like flying shrapnel, crashed through the roofs and set fire to the buildings.

To the conflagration of the sky were added the flames of fire everywhere on earth.

Claps of ear-splitting thunder followed each other incessantly, produced partly by the explosions of the meteors, and partly by a tremendous electric thunderstorm. Rifts of lightning zig-zagged hither and thither.

A continuous rumbling, like that of distant drums, filled the ears of the cowering people below, awaiting their fate. This low rumble was interspersed with the deafening detonations of exploding meteors and the high shriek of hurtling aerial fragments.

Then followed unearthly noises, like the seething of some immense boiling cauldron, the wild wailing of winds, and the quaking of the soil where the earth’s crust was giving way.

This unearthly tempest became so frightful, so fraught with agony and mad terror, that the multitudes grovelling below were overcome with paralysis, and lay prone. Laid low like dumb brutes, they met their doom.

The end of all had come.

_COLOPHON_

_POST HOC, NON PROPTER HOC:
Sic veteres de multis rebus opinabantur,
Eodemque dicto eas jugiter absolvisse
Recte sibi visi sunt,
Vt puta quaecumque et qualiacumque
Cometarum saeculares reditus sequuntur.
CVR TV ITAQVE, forsitan quaeras,
Haec auditu minime jucunda nobis narrasti,
Terrae motus, fluminum inundationes, annonae defectus,
Pestes mortiferas, incendia, bella,
regumque magnorum excidia?
Si tibi cordi est,
LECTOR BENEVOLENTISSIME,
rationem nostram didicisse,
eia, veram accipe:
MVNDVS VVLT DECIPI._

_FINIS._