A COMETARY COLLISION.
ALTHOUGH astronomy is admitted to be the most fasci- nating of the sciences to laymen, a distinction has to be drawn among her triumphs. When shepherds watched their
flocks by night on the vast Chalclan plains, and laid the foundations of astronomy to beguile their long, idle hours, one man was as competent as another to join in their tliversion,—" end often a deal more so." Nowadays, astro. nomy, like her sister sciences, is equipped with mechanical aids whose very comprehension involves years of preparatory study. The story of the discovery of the moons of Mars, planetary specks no larger than London, and divided from us by thirty millions of miles, which not a hundred men in a generation can see, and of the hunting down of Neptune by mathematical analysis which still fewer can properly compre- hend, must be taken by the man in the street as an act of faith. But in compensation astronomy has spectacles which we all can enjoy, of which she announces one of the most gorgeous for the coming week. It has been said by a social philosopher of some repute that a nation's intelligence is in inverse ratio to the amount of money that it spends in pyro- technics, Mexico being his awful example. Whether or not we ought to be ashamed of encouraging the brilliant ingenni- ties of Mr. Brock, certainly no reproach can be levelled against those who sit up through the nights of Tuesday and Wednesday next, on the chance of seeing the magnificent display of celestial fireworks to which we are treated thrice in a century.
It is many hundreds of years since these November meteors, which afford by far the finest of our star-showers, were ob- served by mankind. The earliest certain record of them is that of the night of terror, 902 A.D., when the tyrant Ibrahim lay dying in Sicily, and the heavens rained fire in token of God's anger against the murderer of his brothers and children, so that his heart was changed and he repented before it was too late. There is an earlier Arab account of a wonderful night in the year 599 when the stars shot madly from their spheres "like a swarm of locusts," but there is some doubt as to whether these were the Leonids which we hope to see next week. But scientific attention was first called to these beautiful visitants by Humboldt, who was re- warded for a sleepless night in South America exactly a cen- tury ago by a vision of the Leonid shower raining across the heavens in streaks and spangles of fire during four hours. The previous year two German students had proved that meteors were not the earthly exhalations which they had up till then been held, by observing their flight from different stations, and showing by trigonometry that they were far higher up than the air was then believed to exist. The pre- mise was wrong, but the conclusion was right. In 1883 the Leonid shower came again in such abundance and glory that all through America the negroes thought the end of the world had came, and country farmers looked at the sky next night expecting to see it empty of stars. That year astronomers noticed that all the meteors seemed to come from a single point—the radiant— in the constellation Leo, whence they were named, and our knowledge of star-showers may there be said to begin. Some who remembered Humboldt's description of a similar shower in November, 1799, hit upon the happy idea that the phe- nomenon was periodic, and predicted its return in thirty- three years. On the night of November 13th, 18C6—for the Leonids come nearly a day later on every visit—the expected star-shower returned, lending its chief glories this time to our moonless and happily unclouded British sky. As men watched the "thousands upon thousands of momentary lights with fiery trails, and of many hues, lighting up the landscape and the midnight sky, and spreading often in volleys like fans of rockets over the blue vault, and amidst the stars of heaven," few of them guessed the remarkable develop- ment in our knowledge of the November meteors which was even then preparing. Schiaparelli and Leverrier showed, only two months later, that the orbit of the Leonids wiles huge ellipse stretching out beyond Uranus and touching that of the earth at its nearest point to the sun. The Leonids were a huge swarm of tiny bodies—cosmic dust, as they have well been called—flying round this orbit at a speed nearly double that of the earth, and stringing out so far along it that even at this rate the procession takes nearly three years to pass a given point. Their advance guard arrived last year, and its advent was signalised by the first successful attempt to photograph a star-shower and to dodge the clouds by using stationary balloons for observatories. It is natural to hope that this return of the main swarm may add to our knowledge as much as its two predecessors, although, as we shall probably pass its centre at noon on Wednesday, the best of the show will be lost to us in England. The movements of these meteors cannot, however, be predicted as certainly as those of the planets, and we may hope that Dr. Johnstone Stoney is right in fixing the shower for the small hours of Thursday morning.
Special interest has been given to this recurrence of the *
Leonid star-shower by the Austrian Professor Falb's predic- tion that it will be accompanied by a cometary collision with the earth. Greenwich, indeed, has thrown cold water on the notions of a general conflagration which so sensational a prophecy might arouse in those who remember Poe's mag- niticent imagination of the world's end by a comet. Dr. Falb's comet, the Observatory announces, is not due here till the middle of March, when we shall be about a hundred million miles out of range. But in one sense the melo- dramatic Austrian is right enough ; it is a cometary collision that we are eagerly awaiting next week. At the same time that'ithe orbit of the Leoni ds was being computed in 1866 an independent calculator was working out the path of Tempel's comet. The two results were published within a week, and to the general amazement they almost coincided. This could only mean that there was a physical connection between the comet and the meteors. Schiaparelli next proved the same connection between the August Perseids—the Tears of St. Lawrence—and Swift's comet. Then astronomers began to see that comets were but thick swarms of meteorites, and first cousins of the original nebula, whilst meteor- showers were the debris of ruined comets. What is so rare in astronomy, a specially arranged experimental verification, followed hard on the heels of this bold theory. Biela'a comet had been seen to break into two pieces and then disappear. The earth crossed it former orbit on Novem- ber 27th, 1872, when the comet should have been in the im- mediate neighbourhood : and that night there was a brilliant shower of meteors coming from the direction of Andromeda whence the comet should have come, and christened Andro- medes on this first appearance: they duly returned, having the same period as the defunct comet, in 1892. We now know that the Leonid meteors are the disintegrating portions of the dying Tempel's comet, with which in that sense we shall collide in a day or two. One day they will be spread out along their orbit, no trace of the comet will be left, and there will be a trilling star-shower in the middle of November every year in place of a grand display of celestial fireworks thrice in a century. Such is actually the case with the August Perseids. This hypothesis enables us to trace the history of the Leonids back to the time when they enter ed our system, which Leverrier was bold enough to date 126 A.D. That was too precise but it is as certain as most things in history that some time in the not remote past, probably long after the ap- pearance of man upon the earth, a comet came flying out of remote space, and passed so near the giant planet Uranus that it was captured for good by his attraction, and had to change its wild, straight flight into orbital motion round the sun. Gradually it broke down into a meteor-swarm, until all that is left of it is the telescopic comet in which Dr. Falb is so interested. It is possible that some of the November meteors now and then run the blazing gauntlet of the atmosphere and come to earth, bringing us the cheerful or awful message, as we look at it, that our chemistry is the chemistry of the inconceivably remote worlds whose light takes ten thousand years to reach us,—the most far-reaching example that we know of the Reign of Law. This arouses speculations that there is no room to un- fold here. One may just note that the Leonids are far too recent to have imported that germ of life which, as Lord Kelvin imagines, may thus have reached the cooling earth. Yet all the same, we may look at them with respectful in- terest, if the clouds allow us, not as mere fireworks, but as the nearest approach that moat of us will ever see to the clashing chaos of which our world was made.
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