CHAPTER SEVEN

ORIGIN OF COMETS AND METEORS

(THEORIES ADVANCED BY THE LATE RICHARD A. PROCTOR.)

Among the author’s most treasured possessions is a clipping from the Cincinnati _Daily Gazette_ for February 18, 1874, containing a report of a lecture given by her father, on “Comets and Meteors,” from which the following is an extract:

“In this lecture on comets and meteors, I promised to give some account of what is expelled from the sun when great explosions take place. If I were to say that the comets were shot out from the sun you might be startled, or if I asserted that they were also thrown out of Jupiter and Saturn. But the evidence in connection therewith is very curious. In the first place, we know that matter is shot out from the sun, with a velocity so great as to be carried away from him altogether and so would travel into space. That has only been observed a few times, but the occurrence is probably very frequent. The matter which was expelled, if it struck the earth at all, would strike in the daytime. The side of the earth facing the sun will be the illuminated side. The meteoric matter coming from the sun can only strike the illuminated part, and this can only happen in the daytime. You throw a stone at any object, and it must strike the side of the object you aim at, that is turned toward you. Humboldt affirmed that the largest number of meteoric masses had fallen in the daytime. The larger aërolites have been examined and their microscopic structure studied. Sorby of Sheffield, who examined some of them, says they consist of a number of small globules and were originally in a vaporous state before assuming their present condition. Then came a chemical analysis by Professor Graham and Chandler Roberts of London. They found in the iron of the meteoric mass more hydrogen than iron in a natural condition. Professor Graham said that in his opinion meteors certainly contained iron, and that probably they had been expelled from one of the stars that people space. He drew attention to the fact that stars contained hydrogen in their atmosphere. These are some of the facts concerned with the larger meteoric masses.

“How shall we account for those meteoric streams which travel close to the path of Jupiter? All comets of short period have paths closely approaching some of the large planets. The comet of 1680 went close to Jupiter, long before the explosive power of the sun was noticed. I call them Jupiter’s family of comets. Sir John Herschel said that it was very curious that they had that relation. If we put forward the theory that Jupiter expelled these comets, we have a very startling theory, but many of the theories which have been propounded, some of the most important character and which have been proved to be true, have been the most startling. It is said that as Jupiter, Saturn, and Uranus go along their paths, they draw in the comets which travel close to them, and capture them.

“I made a calculation about the November meteors to see how close they must go to the path of Uranus in order to be captured, and found that they must approach nearly as close as the nearest satellite. Only those which came almost in contact with the planet could be captured. Now, if they were shot out when Uranus was in a sun-like condition, then it would be explained, whereas we find great difficulty in imagining that a comet coming out of space would be captured bodily by a planet like Uranus. Let us consider the matter thus: if comets are expelled from a planet, they will be carried along with the forward motion. If it could appear that some of them went backward, then we would have no evidence of the theory I have been advancing. If most of them travel forward, then we would have some evidence for the theory. Now there is the curious fact that among the comets of short period the whole of Jupiter’s family travel forward. They do not travel in all directions of slope; all have a very moderate slope to the paths of the planets. They do not have the slope even of the asteroids. That is precisely what we notice—that they travel very much with Jupiter. Taking the balance between the two theories—that of expulsion and that of capture—it seems to be in favor of the more startling one—that Jupiter has had the power to expel these objects.”

It is interesting, in connection with this extract from the report of a lecture given by my father some fifty years ago at present time of writing (1925), to turn to a passage in the chapter on comets, by Dr. A. C. D. Crommelin, in the _Splendour of the Heavens_, page 414, where he refers as follows to the capture theory:

“The fact that the members of the Jupiter family (of comets) have direct motion in all cases appears to give a fatal blow to the capture theory. Practically as many comets would approach the planet with retrograde motion as with direct; there is, indeed, the point that those travelling in the same direction as the planet would remain longer in its neighbourhood, and so have more time to be perturbed, which would have some weight; but that out of some fifty comets there is not a single retrograde one is too remarkable a fact to pass over, and it clearly suggests that Jupiter played a different part from that of a mere enslaver, and was concerned with the origin of these bodies in a more intimate manner.

“Many of the considerations I have brought forward were stated by Mr. R. A. Proctor some fifty years ago; they have therefore been accessible to astronomers, who nevertheless have been, as a rule, quite unaffected by them, so that it is time to state them afresh. The consideration that the life of a short-period comet is limited by the rapid wastage to which it is subject by the joint action of the sun and Jupiter was not, I think, so fully realised, when Proctor wrote as it is now. It serves further to invalidate the capture theory, since it prevents our assigning to these bodies such extended lives as that theory demands.”

According to my father’s theory, the giant planets are themselves the parents of their comet-families, and he pictured their birth as having occurred in a remote past, when the planets were more sun-like than they are to-day. We have a great amount of evidence as to the energy of the processes that are at work on Jupiter, as evidenced, for instance, by the great Red Spot (though some have hinted at the possibility of its being an early stage in the formation of a new satellite); Saturn, Uranus, and Neptune also indicate vast upheavals, though distance in their case hinders observation, and even on our own planet we have some striking instances of the power of volcanic energy, as at the eruption of Krakatoa in 1883. Sounds of the explosion were heard three thousand miles away, and a huge volume of dust was blown to the highest regions of the atmosphere, but we are entitled to expect much vaster convulsions in Jupiter, which outweighs the earth three hundred times and is in a much hotter state, judging by the deep envelope of vapours surrounding it, and the rapid changes that are constantly taking place in its appearance, on an enormous scale, as shown by the fine series of photographs which have been obtained of the planet with the giant telescopes.

Writing in his magazine, _Knowledge_, for January 1, 1887, page 64, my father states:

“The theory of ejection was adopted as the only theory by which the chemical, physical, and microscopic structure of meteorites of all orders—from bolosiderites to asiderites—can be accounted for. They were certainly once exposed to such conditions as exist only in the interior of large orbs—suns or planets. And as certainly they have somehow come forth from such interiors. The expulsive force shown by observation to reside in the only sun-like body we can examine, indicates the only way in which such expulsion can conceivably have been effected. Hence, I infer (for my own part I feel assured of the weight of evidence) that all orders of meteorites were expelled from some orbs at some time when such orbs were in the sun-like stage. Generalizing, I include in this theory all orders of meteors, and find all their most characteristic peculiarities explained, and all orders of meteor systems or comets, finding their several orders thus and thus only explicable (if we include all suns now and in the past, all planets in all solar systems, in their past sun-like state, among the sources of meteors and comets). No other general theory seems to me possible.”

Again, in an article in _Knowledge_ for April, 1887, page 135, my father makes the following statement regarding his theory concerning comets and meteors:

“All comets and meteors are sun-born. But it is not to our own sun, nor to those other suns, the stars, that I attribute all comets and meteor systems. Many millions have come doubtless from our sun during the many millions of years he has been a sun, though few of his cometic children are known to terrestrial astronomers. Millions of millions have come from the many millions of suns in our galaxy during the many millions of years of their sun-like existence. But the giant planets were once suns,[11] and in their sun-like state, which must have lasted millions of years, they must have ejected their smaller comets and meteor systems which even now, after millions of years, have paths passing near the orbits of their parent orbs. Our earth and her fellow terrestrial planets had their sun-like stage of life, too, and it must have been while the earth was a sun that the meteors explained specially by Tschermak’s theory were expelled.”

According to his theory, Tschermak, noting the resemblance of structure between meteorites and volcanic products, suggests that meteors of all orders (which would include meteor streams, and therefore comets) were shot out from the earth in the days when she was young. But though this is better than the other theories, in at least suggesting some sort of an origin for comets and meteors, it will not account for comets which do not approach within many millions of miles of the earth’s orbit,[12] and a theory which fails for some among the comets cannot be the true general theory for meteors either.

Mr. Sorby of Sheffield, the eminent mineralogist already referred to, deduced from the microscopic structure of certain meteorites the startling theory that they had once been inside the sun; for there is evidence that their substance once existed in the form of globules of molten metal, which aggregated with large masses, which in turn were exposed to violent friction, indicating conflicting motions of very high velocities.

“Where else,” wrote Sorby, in 1864, “could such conditions exist, except first in the interior, and afterwards in the immediate neighborhood of our sun!” But it is absolutely certain that the theory as thus suggested cannot possibly be true, either as a general explanation of comets and meteors, or even as an explanation of any known meteor system or comet, unless, perhaps, a few of the comets whose orbits pass very near the sun were sun-born, and subsequently disturbed by planetary attractions so as not to return to their parent orb.

According to my father’s views on the subject:

“A flight of meteors shot out from the sun, as Sorby suggested, might have velocity enough to get away from him forever, in which case we should never see a trace of it again, even though we waited for millions of years. If, however, it could not get away, then it must return to its starting-place—that is, back to the sun’s globe—unless, passing near enough to one of the giant planets, it were so far disturbed as only to return by grazing past the sun’s surface. (The comets of 1843, 1880, and 1882, which all traveled in paths near the sun, almost grazing his surface, may well have been parts of a single meteor-flight shot out from his interior millions of years ago.)”

After the appearance of the new comet of 1887 in the southern skies, it was found to be following along the same track as the comets of 1843, 1880, and 1882, thus confirming my father’s theory that these comets were parts of one large comet, dissipated, doubtless, some millions of years ago.

These comets were so bright when near the sun that they could be seen at noon with the naked eye. As regards the heat experienced by the comet of 1843 when near the sun, Sir John Herschel remarked:

“Imagine a glare 25,000 times fiercer than that of an equatorial sunshine at noonday. In such a heat there is no solid substance we know of which would not run like water—boil—and be converted into smoke or vapor.”

[Illustration:

From _Knowledge_

THE SOUTHERN COMET OF JANUARY, 1887 ]

In _Knowledge_ for November 1, 1887, an account is given of the remarkable southern comet first observed in January of that year, and as it is the last article on this topic written by my father for his magazine, giving a more or less detailed account of his views on the subject, the author of this book has deemed it advisable to quote it in full. It is of special interest, not only on account of its giving his theories on the subject, but for the reason that it helps to supply part of the missing chapter on “Comets and Meteors,” which he had planned for his final but unfortunately unfinished work, _Old and New Astronomy_. This work had been in course of preparation for thirty years, and that the material for such a chapter was partially compiled the writer knows from the fact that she has a keen recollection of clippings, MSS., and notes which she saw apparently awaiting classification and arrangement, a short while before her father’s departure from Florida, September 8, 1888. What became of them after his sudden death in New York a few days later, it is impossible to conjecture, unless A. C. Ranyard, who completed the book, found the chapter on comets too difficult to arrange satisfactorily. Yet even the fragments so arduously arranged and collected by my father would have been better than a missing chapter on a subject in which he was so deeply interested and to which he had devoted so much attention.

To return to my father’s account of the comet of January, 1887:

“The comet was first seen by a farmer and a fisherman of Blauwberg, near Cape Town, on the night of January 18–19. The same night it was seen at the Cordoba University by M. Thomé. On the next night Mr. Todd discovered it independently at the Adelaide Observatory, and watched it till the 27th. On the 22d Mr. Finlay detected the comet and was able to watch it till the 29th. At Rio de Janeiro, Mr. Cruls observed it from the 23d to the 25th, and at Windsor, New South Wales, Mr. Tebbutt observed the comet on the 28th and 30th. Moonlight interfered with further observations.

“The comet’s appearance was remarkable. Its tail, long and straight, extended over an arc of thirty degrees, but there was no appreciable condensation which could be called the comet’s head. The long train of light, described as nearly equal in brightness to the Magellanic clouds, seemed to be simply cut off at that end where in most comets a nucleus and coma are shown.

“This comet has helped to throw light on one of the most perplexing of all the puzzles which those most perplexing of all the heavenly bodies, comets, have presented to astronomers. In the year 1668, a comet was seen in the southern skies which attracted very little notice at the time, and would probably have been little thought of since had not attention been directed to it by the appearance and behavior of certain comets seen during the last half-century. Visible for about three weeks, and discovered after it had already passed the point of its nearest approach to the sun, the comet of 1668 was not observed so satisfactorily that its orbit could be precisely determined. In fact, two entirely different orbits would satisfy the observations fairly, though only one could be regarded as satisfying them well.

“This orbit, however, was so remarkable that astronomers were led to prefer the other, less satisfactory though it was, in explaining the observed motions of the comet. For the orbit which best explained the comet’s movements carried the comet so close to the sun as actually to graze his visible surface. Moreover, there was this remarkable and, indeed, absolutely unique peculiarity about the orbit thus assigned: the comet (whose period of revolution was to be measured by hundreds of years) actually passed through the whole of that part of its course during which it was north of our earth’s orbit plane in less than two hours and a half! though this part of its course is a half-circuit around the sun, so far as direction (not distance of travel) is concerned. That comet, when at its nearest to the sun, was traveling at the rate of about 330 miles per second. It passed through regions near the sun’s surface commonly supposed to be occupied by atmospheric matter.

“Now, had the comet been so far checked in its swift rush through those regions as to lose one-thousandth part of its velocity, it would have returned in less than a year. But the way in which the comet retreated showed that nothing of this sort was to be expected. I am not aware, indeed, that any anticipations were ever suggested in regard to the return of the comet of 1668 to our neighborhood. It was not till the time of Halley’s comet, 1682, that modern astronomy began to consider the question of the possibly periodic character of cometic motions with attention. (For my own part, I reject as altogether improbable the statement of Seneca that the ancient Chaldean astronomers could calculate the return of comets. The comet of 1680, called Newton’s, was the very first whose orbital motions were dealt with on the principles of Newtonian astronomy, and Halley’s was the first whose periodic character was recognized.)

“In 1843, another comet came up from the south, and presently returned thither. It was, indeed, only seen during its return, having, like the comet of 1668, been discovered only a day or two after perihelion passage. Astronomers soon began to notice a curious resemblance between the orbits of the two comets. Remembering the comparative roughness of the observations made in 1668, it may be said that the two comets moved in the same orbit, so far as could be judged from observation. The comet of 1843 came along a path inclined at apparently the same angle to the earth’s orbit plane, crossed that plane ascendingly at appreciably the same point, swept round in about two hours and a half that part of its angular circuit which lay north of the earth’s orbit plane, and, crossing that plane descendingly at the same point as the comet of 1668, passed along appreciably the same course towards the southern stellar regions! The close resemblance of two paths, each so strikingly remarkable in itself, could not well be regarded as a mere accidental coincidence.

“However, at that time no very special attention was directed to the resemblance between the paths of the comets of 1843 and 1668. It was not regarded as anything very new or striking that a comet should return after making a wide excursion round the sun; and those who noticed that the two comets really had traversed appreciably the same path around the immediate neighborhood of the sun, simply concluded that the comet of 1668 had come back in 1843, after 175 years, and not necessarily for the first time.

“It must be noticed, however, before leaving this part of the record, that the comet of 1843 was suspected of behaving in a rather strange way when near the sun. For the first observation, made rather roughly, indeed, with a sextant, by a man who had no idea of the interest his observations might afterwards have, could not be reconciled by mathematicians (including the well-known mathematician, Benjamin Pierce) with the movement of the comet as subsequently observed. It seemed as though when in the sun’s neighborhood the comet had undergone some disturbance, possibly internal, which had in slight degree affected its subsequent career.

“According to some calculations the comet of 1843 seemed to have a period of about thirty-five years, which accorded well with the idea that it was the comet of 1668, returned after five circuits. Nor was it deemed at all surprising that the comet, conspicuous though it is, had not been detected in 1713, 1748, 1783, and 1818, for its path would carry it where it would be very apt to escape notice except in the southern hemisphere, and even there it might quite readily be missed. The appearance of the comet of 1668 corresponded well with that of the comet of 1843. Each was remarkable for its long tail and for the comparative insignificance of its head. In the northern skies, indeed, the comet of 1843 showed a very straight tail, and it is usually depicted in that way, whereas the comet of 1668 had a tail showing curvature. But pictures of the comet of 1843, as seen in the southern hemisphere, show it with a curved tail, and also the tail appeared forked toward the end, during that part of the comet’s career. However, the best observations, and the calculations based on them, seemed to show that the period of the comet of 1843 could not be less than 500 years.

“Astronomers were rather startled, therefore, when, in 1880, a comet appeared in the southern skies which traversed appreciably the same course as the comets of 1668 and 1843. When I was in Australia in 1880, a few months after the great comet had passed out of view, I met several persons who had seen both the comet of that year and the comet of 1843. They all agreed in saying that the resemblance between the two comets was very close. Like the comet of 1843, that of 1880 had a singularly long tail, and both comets were remarkable for the smallness and dimness of their heads. One observer told me that at times the head of the comet could barely be discerned.

“Like the comets of 1668 and 1843, the comet of 1880 grazed close past the sun’s surface. Like them it was but about two hours and a half north of the earth’s orbit plane. Had it only resembled the other two in these remarkable characteristics, the coincidence would have been remarkable. But of course the real evidence by which the association between the comets was shown was of a more decisive kind. It was not in general character only, but in details that the path of the comet of 1880 resembled those on which the other two comets had traveled. Its path had almost exactly the same slant to the earth’s orbit plane as theirs, crossed that plane ascendingly and descendingly at almost exactly the same points, and made its nearest approach to the sun at very nearly the same place.

“To the astronomer such evidence is decisive. Mr. Hind, the superintendent of the _Nautical Almanac_, and as sound and cautious a student of cometic astronomy as any man living, remarked, so soon as the resemblance of these comets’ paths had been ascertained, that if it were merely accidental the case was most unusual; nay, it might be described as unique. And, be it noticed, he was referring only to the resemblance between the comets of 1880 and 1843. Had he recalled at the time the comet of 1668, and its closely similar orbit, he would have admitted that the double coincidence could not possibly be merely casual.

“But this was by no means the end of the matter. Indeed, thus far, although the circumstances were striking, there was nothing to prevent astronomers from interpreting them as other cases of coincident, or nearly coincident, comet paths, had been interpreted. Hind and others, myself included, inferred that the comets of 1880, 1843, and 1668 were simply one and the same comet, whose return in 1880 probably followed the return in 1843 after a single revolution.

“In 1882, however, two years and a half after the appearance of the comet of 1880, another comet came up from the south, which followed in the sun’s neighborhood almost the same course as the comets of 1668, 1843, and 1880. The path it followed was not quite so close to those followed by the other three as these had been to each other, but yet was far too close to indicate possibly a mere casual resemblance; on the contrary, the resemblance in regard to shape, slope, and those peculiarities which render this family of comets unique in the cometary system, was of the closest and most startling kind.

“Many will remember the startling ideas which were suggested by Professor Piazzi Smyth respecting the portentous significance of the comet of 1882. He regarded it as confirming the great pyramid’s teaching (according to the views of orthodox pyramidalists) respecting the approaching end of the Christian dispensation. It was seen under very remarkable circumstances, blazing close by the sun, within a fortnight or three weeks of the precise date which had been announced as marking that critical epoch in the history of the earth.

“Moreover, even viewing the matter from a scientific standpoint, Professor Smyth (who, outside his pyramidal paradoxes, is an astronomer of well-deserved repute) could recognize sufficient reason for regarding the comet as portentous. Many others, indeed, both in America and in Europe, shared his opinion in this respect. A very slight retardation of the course of the comet of 1880, during its passage close to the surface of the sun, would have sufficed to alter its period of revolution from the thirty-seven years assigned on the supposition of its identity with the comet of 1843, to the two and a half years indicated by its apparent return in 1882, and if this had occurred in 1880, a similar interruption in 1882 would have caused its return in less than two and a half years.

“Thus, circling in an ever-narrowing (or rather shortening) orbit, it would presently, within a quarter of a century or so, perhaps, have become so far entangled among the atmospheric matter around the sun, that it would have been unable to resist absolute absorption. What the consequences to the solar system might have been none ventured to suggest. Newton had expressed his belief that the effect of such absorption would be disastrous, but the physicists of the nineteenth century, better acquainted with the laws associating heat and motion, were not so despondent. Only Professor Smyth seems to have felt assured (not being despondent but confident) that the comet portended, in a very decisive way, the beginning of the end.

“However, we were all mistaken. The comet of 1882 retreated on such a course, and with such variation of velocity as to show that its real period must be measured not by months, as had been supposed, nor even by years, but by centuries. Probably it will not return till 600 or 700 years have passed. Had this not been proved, we might have been not a little perplexed by the return of apparently the same comet in this present year (1887). A comet was discovered in the south early in January, whose course, dealt with by Professor Kruger, one of the most zealous of our comet calculators, is found to be partially identical with that of the four remarkable comets we have been considering. Astronomers have not been moved by this new visitant on the well-worn track, as we were by the arrival of the comet of 1882, or as we should have been if either the comet of 1882 had never been seen, or its path had not been shown to be so wide ranging. Whatever the comet of the present year may be, it was not the comet of 1882 returned. No one even supposes that it was the comet of 1880, or 1843, or 1668. Nevertheless, rightly apprehended, the appearance of a comet traveling on appreciably the same track as those four other comets is of extreme interest, and indeed practically decisive as to the interpretation we must place on these repeated coincidences.

“Observe, we are absolutely certain that the five comets are associated together in some way; but we are as absolutely certain that they are not one and the same comet which had traveled along the same track and returned after a certain number of circuits. We need not trouble ourselves with the question whether two or more of the comets may not have been in reality one and the same body at different returns. It suffices that they all five were not one; since we deduce precisely the same conclusion whether we regard the five as in reality but four or three or two. But it may be mentioned, in passing, as appearing altogether more probable, when all the evidence is considered, that there were no fewer than five distinct comets, all traveling on what was practically the selfsame track when in the neighborhood of the sun.

“There can be but one interpretation of this remarkable fact—a fact really proved, be it noticed (as I and others have maintained since the retreat of the comet of 1882), independently of the evidence supplied by the great southern comet of the present year. These comets must all originally have been one comet, though now they are distinct bodies. For there is no reasonable way (indeed no possible way) of imagining the separate formation of two or more comets at different times, which should thereafter travel in the same path.

“No theory of the origin of comets ever suggested, none even which can be imagined, could account for such a peculiarity. Whereas, on the other hand, we have direct evidence showing how a comet, originally single, may be transformed into two or more comets traveling on the same, or nearly the same, track.

“The comet called Biela’s, which had circuited as a single comet up to the year 1846 (during a period of unknown duration in the past—probably during millions of years), divided then into two, and has since broken up into so many parts that each cometic fragment is separately indiscernible. The two comets into which Biela’s divided, in 1846, were watched long enough to show that, had their separate existence continued (visibly), they would have been found, in the fullness of time, traveling at distances very far apart, though on nearly the same orbit. The distance between them, which in 1846 had increased only to about a quarter of a million of miles, had in 1852 increased to five times that space.

“Probably a few thousand years would have sufficed to set these comets so far apart (owing to some slight difference of velocity, initiated at the moment of their separation) that when one would have been at its nearest to the sun, the other would have been at its farthest from him. If we could now discern the separate fragments of the comet, we should doubtless recognize a process in progress by which, in the course of many centuries, the separate cometic bodies will be disseminated all round the common orbit. We know, further, that already such a process has been at work on portions removed from the comet many centuries ago, for as our earth passes through the track of this comet she encounters millions of meteoric bodies which are traveling in the comet’s orbit, and once formed part of the substance of a comet doubtless much more distinguished in appearance than Biela’s.

“There can be little doubt that this is the true explanation of the origin of that family of comets, five of whose members returned to the neighborhood of the sun (possibly their parent) in the years 1668, 1843, 1880, 1882, and 1887. But it is not merely as thus explaining what had been a most perplexing problem that I have dealt with the evidence supplied by the practical identity of the orbits of these five comets. When once we recognize that this, and this only, can be the explanation of the associated group of five comets, we perceive that very interesting and important light has been thrown on the subject of comets generally.

“To begin with, what an amazing comet that must have been from which these five, and we know not how many more, were formed by disaggregative processes—probably by the divellent action of repulsive forces exerted by the sun! Those who remember the comets of 1843 and 1882 as they appeared when at their full splendor will be able to imagine how noble an appearance a comet would present which was formed of these combined together in one. But the comet of 1880 was described by all who saw it in the southern hemisphere as most remarkable in appearance, despite the faintness of its head. The great southern comet of the present year (1887) was a striking object in the skies, though it showed the same weakness about the head. That of 1668 was probably as remarkable in appearance as even the comet of 1882. A comet formed by combining all these together would certainly surpass in magnificence all the comets ever observed by astronomers.

“And then, what enormous periods of time must have been required to distribute the fragments of a single comet so widely that one would be found returning to its perihelion more than two centuries after another! When I spoke of one member of the Biela group being in aphelion, when another would be in perihelion, I was speaking of a difference of only three and one-third years in time; and even that would require thousands of years. But the scattered cometic bodies which returned to the sun’s neighborhood in 1668 and 1887 speak probably of millions of years which have passed since first this comet was formed. It would be a matter of curious inquiry to determine what may have been the condition of our sun, what even his volume, at that remote period in history.”

In view of our present knowledge of the status of the sun as a comparative dwarf in the stellar system, may it not have been a giant star at that remote period of its existence above referred to, rivaling in volume the giant star Betelgeuse with its diameter exceeding two hundred million miles.[13] At that period of the evolution of the sun, how terrific must have been the force of the upheavals which rent its surface, flinging forth cometic material with incalculable speed, to distances far exceeding any known in connection with the comets with which we are familiar.

Regarding the solar origin of comets, Dr. A. C. D. Crommelin writes as follows in _Splendour of the Heavens_, page 407:

“When we note that the orbit of the great comet of 1882 almost grazes the sun’s surface, there is a natural tendency to attribute a solar origin to it. We know from the phenomena of the solar prominences that the sun is continually erupting torrents of matter with very high speeds; a speed of 270 miles per second would suffice to send the matter round the sun in a circular orbit; if it rose to 382 miles per second the orbit would be parabolic; while for any intermediate speed it would be elliptic. By combining the observed speed of ascent of the prominence matter with the speed of approach or recession that is indicated by the shift of the lines in the spectrum, we conclude that speeds of this order are quite common, so that no difficulty arises on that account. I feel rather more difficulty from the consideration that the meteoric masses that compose a comet’s head could not exist in the sun in a solid state; the heat would suffice to vaporize them. The materials would solidify in the cold of space, but as they would be under no pressure, I imagine that the resulting solid particles would be microscopically small, not of the size required to form reservoirs for a large amount of gas. All objects ejected by the sun would move in orbits that intersect the sun, except in so far as their orbits are modified by planetary action. This latter might readily be large enough to change the orbit to one just outside the sun (like those of the sun-grazing comets of 1680, 1843, 1882, etc.). However, the great majority of known comets have orbits whose least distance from the sun is so large that we cannot imagine an origin for these by simple solar eruption.

“The question arises, Can the comets have existed for so long a period in view of the wastage that they undergo? According to the geologists the date of the approach of another sun to ours (as suggested in the planetesimal hypothesis) must be put at least a thousand million years ago; in such an interval, even the comets of longest period would have returned thousands of times, and I gravely doubt whether they could continue to be such compact bodies as they appear to be; I frankly admit that I have no plausible suggestion to offer for evading the difficulty; it is one of the numerous cases in astronomy (the status of the spiral nebulæ is another) in which we must be content for the present to record observed facts and suggested interpretations, leaving full understanding to come at a later date, if at all.”

According to the same authority, in connection with his views on the subject, as expressed after reading the MSS. prepared for this chapter, he writes, as follows:

“I have noted a paper by A. A. Newton (see _Observatory_ for 1894, page 250), in which he says, that out of 1,000 million comets approaching the sun, 126 comets will have periods reduced to 6 years, 839 to 12 years, 1,701 to 18 years, and 2,670 to 24 years. Further, of the 839 no less than 203, or a quarter of the whole, will have retrograde orbits after perturbation. I think these results go very strongly against the capture hypothesis. There would only be one short-period comet in something like 2 million years; whereas the experience of Biela’s, Brorsen’s (and perhaps also Tempel 1 and Holmes), suggests that several of them have become extinct in a century, so an equal number of new ones is required to keep up the supply. It is a matter of surprise to me that the difficulty is not more generally recognized.”

The following brief abstract, condensed from an article written by Professor W. W. Payne, for _Popular Astronomy_, April, 1906, page 221, regarding “Jupiter’s Family of Comets,” with accompanying chart, may be of interest in connection with the matter under discussion in this chapter:

“This notable family of comets is more and more of a wonder, the further its study is pursued. It is remarkable on account of its size, and—if the capture theory be correct—of the power of Jupiter to capture comets and make them members of his family, if they, in their wild flights through space, happen to come too near to him as they sometimes do in certain parts of his orbital path around the sun. But a close study of the chart showing the paths of Jupiter’s family of comets would seem to indicate that nearly all the farthest points of the comet’s orbits from the sun are on one side of Jupiter’s orbit. These points are marked by short cross lines. Now if Jupiter obtained his family by capture, why should he be more successful on one side of the orbit than the other?

Moreover, the motions of all these bodies about the sun, and about Jupiter, are direct, that is, contrary to those of the hands of a watch. Does not this fact of the comets traveling in the same direction, point to the supposition that they were originally ejected from the planet rather than that they were captured by Jupiter?”