The fairy tales of science/A Tale of a Comet
A Tale of a Comet.
"I could a Tale unfold."—Hamlet.
What I am? What I am made of? What class or family of celestial bodies do I belong to? How many there are of us? Where do we come from? Where are we going to? What offices do we perform—what purpose subserve in the great economy of the heavens? Tell you all about us?—Well, you are inquisitive, my little terrestrial friends, and it appears to me, a little overmuch so; and small information, I trow, will you get out of me on most of these points. Still, I cannot but admire the indomitable perseverance with which you are prying into the abyss of space, seeking to fathom the secrets of the universe; and although some of you have of late rather offended the dignity of the great family to which I belong, denying us even the possession of anything like a substantial body,—calling us "visible nothings"—affirming that they know all about us, that they can look right through us, and giving us somewhat plainly to understand that they regard us very much in the light of exploded humbugs, I yet will bear no malice, and will endeavour, not, indeed, to satisfy your curiosity in all matters concerning me and my brethren, but to give you some few scraps of information and stray hints about us, leaving you to make the best use of them you may, in your interminable cruise on the endless sea of speculation.
Well, then, I am one of a most numerous family. Johannes Kepler—one of those bright intellectual stars that adorn and illumine your microscopic mite of a sphere, and render it interesting even to the giants of creation—declared that “there are more comets in space than fishes in the ocean.” A kindred spirit, a Kepler of the present age—Arago—has calculated our number at some three and a half millions at the lowest computation, and possibly twice as many. We are of all sizes and magnitudes, from the incredibly immense down to the minutest telescopic. I myself may boast of a bulk exceeding that of the sun in the proportion of nearly 300 to 1; that of your planet in the proportion of 400,000,000 to 1. My brother of 1811 was still larger, being about 600,000,000 times the bulk of your earth! The essential part about us is the nucleus, which sometimes appears as a bright stellar point, and sometimes rather gives the notion of a planetary disc, seen through a nebulous haze. What is generally called our head, is simply this nebulous haze which surrounds the nucleus; the train of illuminated vapour which is often, though by no means always, attached to the head, is usually termed by you the tail, though, allow me to observe, rather improperly, since this appendage often precedes us in our motions. The inhabitants of that portion of your sphere which is designated in your maps by the name of China—who, though certainly a little pigheaded, and strangely averse to progress in arts and sciences, are yet very careful, and, moreover, much more ancient observers of the starry heavens than you Europeans—have bestowed upon this occasional appendage the much more appropriate and significant name of brush or pencil of light. The nebulous haze which invariably surrounds the nucleus of members of our family is called the coma, from a Greek word signifying hair; some fancied resemblance of the nebulous matter composing this coma and the tail, has gained us the name of comets, or hairy stars. Now, though rather put out by M. Babinet’s most unceremonious and very unhandsome statement respecting the extreme “flimsiness” of our material structure, I am yet bound to confess that there is, unfortunately, a great deal of truth in it. Leaving altogether out of the question the physical constitution of what is termed our tail, which truly immeasurably exceeds in tenuity the atmosphere surrounding your earth, I must even “plead guilty” to the charge of extreme “light-headedness” brought against us. I would deny it if I could, but I know it would be of no use; as you are but too well aware that even the faintest stars can often be distinctly seen, without any perceptible diminution of their lustre, through the very centre of our heads, which, considering the enormous bulk, for instance, of my brother’s head of 1811—exceeding that of your earth in the proportion of 4,000,000 to 1—most clearly shows that the matter composing it must possess an extreme degree of tenuity. If additional proof were required of this patent fact, it might be found in the almost imperceptible power of attraction which we, even of the largest magnitudes, exercise upon Jupiter and other planets, or even upon their satellites, and those still smaller atomic mites, the planetoids, when we accidentally cross them in their orbits. Jupiter more especially, who seems to have a peculiar knack of being always, somehow or other, in the way of some of us, is not in the least affected by pretty near contact with our immense bulk, and actually often manages to thrust us right out of our orbits—a feat which even the wretched little planetoids, of whom myriads might find room in the head, millions in the tail, of one of us, have sometimes succeeded in performing. I would not, however, have you believe that we are mere “visible nothings”—the “airy offspring of vapour and the sun;” however so attenuated the material composing us may be, still it is ponderable matter; and there can be no doubt but that in some of us at least, the nucleus consists of a solid body of appreciable density, a direct collision with which it would not be over wise in any planet to court. Not that I want to frighten you about the possibility of such a collision with your earth; your wise men have cleverly calculated that there are about 300,000,000 chances against a contingency of the kind. Moreover, depend upon it, none of us is likely ever to seek the chance of a brush against your earth or any other planet—and that for a sufficient reason of our own. You remember, perhaps, one of your very clever men—who, however, for all that, are by no means exempt from occasional mistakes—Mr. George Stephenson, whose genius has enabled you, poor little mites, to crawl at a somewhat less snailly pace than of old over the surface of your cheese, once said, in reply to a question addressed to him as to whether it might not be awkward if a cow were to happen to stray on a line of rails, right in the way of a rapidly-advancing train, “Yes, very awkward—for the coo!” Experience has since but too often and too clearly proved that an event of the kind may be equally “awkward” for the train as for the cow; and we, who are much wiser in our generation, have really no notion of tempting the chances of a collision that might prove equally fatal to the two bodies.
I may here briefly observe, that the material of which we are composed is not luminous in itself, but is illuminated by the sun of this, or, in the case of those of us who soar into the immensity of space, some other solar system.
We are most capricious and mutable in the forms which we assume, though, as a general rule, our heads mostly affect the globular or spheroidal shape. The magnificent luminous appendages or tails which many of is proudly display, are sometimes straight, and sometimes curved like a scimitar. With some of us this vapoury train of light attains an immense apparent length. Thus, for instance, my brother comet of 1811—which, by-the-bye, when first seen, possessed no visible tail—speedily threw out a luminous appendage covering some 25 degrees of heaven, or some 130,000,000 of miles. My own tail stretches some 11 degrees beyond this; that of my brother of 371 B.C., Aristotle tells you, occupied some 60 degrees of the heavens; that of the Comet of 1680 covered between 70 and 90 degrees; and that of the Comet of 1618 is stated to have extended to 104 degrees in length!
Some of us exhibit more than one tail. My brother of 1744, for instance, had no less than six, spread out like an immense fan, extending to a distance of nearly 30 degrees in length. I have just now mentioned that my brother of 1811 was not at first provided with an appendage of luminous vapour. This is often the case with us. Thus the great Comet of 1843 showed at its first appearance simply a nucleus, surrounded by a coma; but it speedily set about supplying the deficiency, and in less than twenty days managed to throw out a most magnificent tail, measuring two hundred millions of miles, which was generated, accordingly, at the rate of 10,000,000 miles a day, the matter composing it being propelled through space with a velocity of 115 miles per second, which is nearly six times that of the earth in its orbit, and two hundred and fifty times greater than that of a cannon-ball!
You are already aware, so I need hardly tell you, that we are all of our family most eccentric in our motions. To superficial observation we would indeed seem to be careering with mad capriciousness along the great highway of space. But if you watch our motions more closely, you will find that there is the strictest method in this apparent madness of our movements, and that we obey the same universal law of attraction and gravitation as the other celestial bodies—some of us moving about the sun in parabolic orbits, or at least in ellipses of various degrees of eccentricity, and returning in determinate periods in the same path (unless disturbed); others running off in hyperbolic orbits, to visit other systems in the immensity of space. Most of us come, in fact, into this solar system from parts of the universe extending to enormous distances beyond its limits, and after approaching more or less near to the sun, start off again on our journey to distances not less remote. I may, perhaps, be permitted here to observe that, with all due deference to M. Babinet, and his somewhat contemptuous opinion of us and our uses, I can safely affirm that we subserve some better and higher purpose in the great economy of the universe than enabling your astronomers to verify certain natural laws, and to pry into the mysteries of heaven. You will not, of course, expect me to tell you what these purposes may happen to be—depend upon it, you will find this out all in good time, by the unaided efforts of that marvellous intelligence with which it has pleased the Almighty to endow you. This much, however, you may take for granted even now, that we serve as means of communication between system and system. May it not be, also, that we serve to gather in our path the detritus of old worlds, to be moulded hereafter into new spheres?—that we serve to carry to the suns of this and other systems the ardent fires with which we get impregnated in our passage near Sirius and myriads of other suns?—that we serve to waft beings that have passed their probation, from worlds immeasurably brighter than yours, to spheres infinitely more glorious than theirs? What a boundless field of speculation is open here to the human mind!—of exalted speculation, such as may befit the grandeur of the subject, and the vast intellectual powers of man, and may henceforward take the place of the absurd notions of our influence for good or evil to which the superstitious feelings of mankind in the darker ages, and even in more modern and “enlightened” times, had given birth. It seems hardly credible now that our apparition in the heavens should ever, at any period of time, have been almost universally regarded with feelings of awe and terror, and that to us should have been ascribed the most malignant influences, and a most astonishing diversity of effects, physical, physiological, social, and political. And passing strange that even men like Johannes Kepler should not have been entirely free from this weakness! Seneca alone among ancient philosophers dared to oppose his powerful logic to the superstitious ideas which his age, and the ages that had preceded it, entertained with regard to our apparition in the heavens. He, that marvellous double and counterpart of the great British philosopher of a later period— Bacon, equally wise, equally mean—declared that we moved regularly in orbits fixed by natural laws, and expressed his conviction that posterity would one day stand aghast at the blindness of his age, which could ignore or disregard facts so clear and palpable.
One of the brightest of our family—so bright, indeed, as to be plainly visible in the daytime, happening to make its appearance in the year 44 or 43 B.C., a short time before or after the assassination of Cæsar—was held to have, if not actually brought about the death of the aspiring dictator, at all events predicted or attended it—as if the heavens would be likely to take an interest in the life or death of such a “thing of blood and mire!”
Another Comet—the first whose orbit was calculated, in 1682, by your illustrious Edmund Halley, whose name it bears, and will hand down to the remotest ages—had, at one of its former appearances, in June, 1456, spread terror throughout Europe. It was regarded as a most powerful ally of the Turkish Sultan, Mohammed II., who had taken Constantinople, and threatened to overrun Christian Europe with his victorious armies. Pope Calixtus II. thought it high time to come to the aid of his sorely-pressed flock, and launched the thunders of the Vatican against the celestial visitor, who thereupon (in due course of time) disappeared from the heavens; the Pope, in order to perpetuate this startling manifestation of the power of the Church, decreeing and ordaining the bells to be rung at noon, a custom observed to the present day in Catholic countries. What a curious commentary this doth afford on the “infallibility” which the Bishops of Rome dare arrogate to themselves!
Another of my brethren—the very one, in fact, whom you have been so anxiously expecting to reappear ever since February, 1848, but who, according to Bomme’s calculation, will only rejoice you sometime about 1860 by a sight of his splendid dimensions—terrified the Emperor Charles V., in 1556, into consummating the abdication of all his earthly crowns, and retirement to a monk’s cell in the cloister of St. Justus, in Spain, where he who, in the pride and arrogance of power, had sought, though vainly indeed, to make the millions who obeyed his sceptre conform to his own most narrow and bigoted religious creed, and in his presumptuous vanity had imagined that Heaven’s Great Lord had condescended to send a comet by way of special messenger to him, discovered, though unfortunately rather too late, that he could not even make two clocks strike alike and at the same time, and felt humbled to the dust thereat.
But enough of these instances of the presumption and folly of your kind,—which yet are, perhaps, less insulting, after all, to the dignity of our family than the notion that we occasionally take a delight in killing cats, as the splendid Comet of 1668 was accused of doing in Westphalia; or blinding flies, destroying wasps, and cursing poor Whitechapel shoemakers with four babies at a birth! or destroying cities by an earthquake, knocking down steeple clocks in Scotland, and indulging in other undignified vagaries of the kind!
I have some personal reason, if I may be allowed the expression, to take a special interest in the fair fame of the Comet of 1668, as there would appear to be some chance that I may in the end turn out to be identical with that splendid object, to whom a period of 16 years has been assigned, and whose last recorded appearance bears date 1843. Mind, I do not mean to assert anything positive about this matter, which resolves itself simply into a question of identity. I know that there is an individual of your species waiting for me now at the Cape of Good Hope, who will bring his powerful reflector, and equally powerful intellect, to bear upon me; and you may well afford to wait till next spring, when you will most probably learn from that quarter whether I am the real Simon Pure of 1668, with a period of 16 years, or have a period of something like 150 times as long. At all events, surely, where learned astronomers disagree, you would not ask a poor Comet like me to decide!
Even so recently as 1829, a most learned English medical practitioner, a Mr. T. Forster, made a fierce onslaught on the character of Comets in general, to whom he ascribes all imaginable malignant influences, such as epidemic diseases of all kinds, earthquakes, volcanic eruptions, floods, droughts, and famines!
Now, you may believe me, my little friends, we are entirely innocent of these dreadful charges brought against us; and I grieve to add, we cannot properly claim credit either for the glorious seasons that will occasionally coincide with our appearance, and for the splendid harvests of corn and wine produced therein. It would unquestionably have been a proud distinction for me to have had my name associated, as was that of my illustrious predecessor of 1811, with the wine of this most splendid and abundant year 1858; but truth will not be trifled with: careful statistical researches and comparisons of thermal and cometary observations, extending over a period of a century, have but too fully established the conclusion that we can claim no influence whatsoever on the temperature of the seasons. It is your Mr. Arago who has dealt us this heavy blow and great discouragement.
I will now, in conclusion, add a few more words about some of the most remarkable of my brethren, whose periods have been fixed with more or less precision.
The most remarkable of these is the great Comet known by.the name of Halley’s, from the circumstance of that illustrious geometer, as has already been mentioned, having predicted its return. The immortal Newton having demonstrated the possibility of any conic section whatever being described about the sun, by a body revolving under the dominion of the law of gravitation, applied his theory to the great Comet of 1680 with the most complete success. He ascertained that this Comet described about the sun as its focus an elliptic orbit of such exceeding eccentricity as to degenerate into a parabola, and that in this orbit the areas described about the sun were, as in the planetary ellipses, proportional to the times. Two years after, in the year 1682, Halley applied the principles of the Newtonian theory to cometary bodies, and calculated thereby the orbits of several ancient comets, which led him to the discovery of a remarkable coincidence in the elements of the orbits of certain comets which had been observed at nearly equal intervals of time in 1531, 1607, and 1682. After mature consideration, he concluded that these comets must be identical, returning at certain fixed periods, and ventured to predict another return about the year 1759. Clairaut, an eminent mathematician of the period, undertook to calculate the delay which the return of this comet would experience from the disturbing influence exercised upon its orbit by the larger planets, and fixed the return for spring, 1759. True to the appointment, the Comet made its reappearance on the 12th of March of that year, and once more 76 years after—in October, 1835—as had been calculated by several eminent mathematicians.
The great Comet which appeared in 1680 is supposed to have a period of 575 years, and to be identical with the Comets seen in 1105 and 575, and also with that seen in 44 or 43 B.C., of which mention has already been made.
Another great Comet—the one which, as I have told you, frightened poor Charles V. in 1566, and is expected to reappear in 1860—is held to be identical with certain comets observed in 104, 683, 975, and 1264, to which latter attaches the reputation of having presaged the death of Pope Urban IV., who died on the 2nd October, just when that Comet was making its last appearance in the heavens.
Another, again, which appeared in 1661, is supposed to be the same as that seen in 243, 891, 1145, 1402, and 1532.
The Comet discovered by Olbers, in 1815, in the constellation Musca, has a period of 74 years. Some of our family revolve in comparatively short periods round the sun. One of the most remarkable of these is the one called Encke’s Comet—so named from Professor Encke, of Berlin, who first ascertained its periodical return. This Comet revolves round the sun in the short period of 31 years; it has been observed in 1786, 1795, 1805, 1818, and regularly ever after, there being, however, a very strange and anomalous circumstance connected with it—viz., that its periods of revolution are found to be successively and equably shorter, a circumstance which forebodes its ultimate fall into the sun, unless it should previously be dissipated altogether—a termination of its career by no means unlikely, and to which many members of our family are liable.
Another Comet of short period is the one called after Mr. Biela, of Josephstadt, who, at its apparition in 1826, identified it with Comets that had appeared in 1772 and 1805. The time of its revolution is about 62 years. It has since been observed in 1832, 1839, 1845-6, and 1852—in the two last years as a double Comet.
A Comet discovered by M. Faye, in 1843, describes an elliptic orbit in a period of 71 years, and has been observed on its return in 1850.
Two other Comets—the one discovered by De Vico, in 1844, the other by Brorsen, in 1846—have each a period of about 51 years. Another, finally, discovered by d’Arrest, in 1851, in the constellation Pisces, has a period of 7 years.
Before I take my final leave of you, I may still mention that, though now universally known as “Donati’s Comet,”—Professor Donati, of Florence, enjoying the credit and reputation of having “sighted” me first, on the 2nd June, 1858—a reclamation has been put in by Dr. Winneke, of Bonn, who declares having discovered me as early as the 9th March; and by Father Neslhuber, Director of the Kremsmünster Observatory, who professes to have seen me in the constellation Aquila, on the 19th March. Dr. Bruhns, of Berlin, has calculated that I complete my revolution round the sun in an eccentric ellipse, in a period of 2,100 years; my greatest distance from the sun, which it will take me 1,050 years to reach, being about 31,506,000,000 miles.
And now, farewell! till our next meeting. Methinks I hear you exclaim, that this is scant and meagre information indeed. Patience, my little friends; at my next appearance—whenever that may be—I trust I may be in a position to tell a different and more circumstantial and satisfactory “Tale of a Comet.”
- M. Babinet, a distinguished French philosopher, in his "Études et Lectures sur les Sciences d'Observation," is indeed rather hard upon the poor comets. He calls them mere gatherings of vapour, visible nothings, devoid of all physical properties, incapable of doing either good or harm, and useful simply through enabling us to verify Newton’s law of attraction, and explore the regions of heaven far beyond the limits of the solar system. He says science now knows all about them, and the public have ceased taking the least interest in them. It would be interesting to know whether M. Babinet has since seen reason to modify this somewhat contemptuous opinion of those “strange wanderers of the sky.” Certain, however, it is, that science confessedly knows as yet very little about comets, and that the apparition and passage of Donati’s Comet in 1858 has been narrowly watched and tracked with the most eager curiosity, and with the most lively interest.
- We must here assume the reader to know that an ellipse whose major axis is of infinite length, is said to degenerate into a parabola. The parabola is that conic section which forms the limit between the ellipse on the one hand, which returns into itself, and the hyperbola on the other, which runs out to infinity.
- At the return of Biela’s Comet, in 1845-6, a most singular phenomenon was observed. The Comet appeared at first, as usual, as a single body; but on its approach towards perihelion it was, on the 13th January, 1846, for the first time, seen to be attended by another Comet considerably fainter, at a distance of about 2′. This distance continued steadily to increase, with a corresponding change in the comparative brightness of the two Comets, till the companion Comet became as bright as the original, and subsequently brighter, exhibiting a star-like nucleus; a very short time after, however, the original Comet gained again in brilliancy on its companion, which finally disappeared some time before the other ceased to be observed.