THE SOLAR SYSTEM.

Lyttelton Times, Volume CXV, Issue 16487, 28 February 1914, Page 16

THE SOLAR SYSTEM.

Six Lectures given by R. A. PROCTOR during the month of January, 1874, in the United States. TITLES: 1. "THE SUN,” Part I. “THE SUN," Port 11. 8. "THE SUN’S FAMILY OF PLANETS," Part I. “THE SUN’S FAMILY OF PLANETS,” Part 11. "COMETS AND METEORS.” 6. “ THE MOON."

The Lcoturos aro oopied, revised end brought up-to-date by his daughter, MISS MARY PROCTOR, and now are re-publi»hcd for the first time.

COMETS AND METEORS

The subject I have to deal with tonight is full of mysteries and great discoveries made in connection with these celestial wanderers. We have, to begin with, tho great wonder that comets and meteors should be associated in any way, for they are so unlike each other. Comets are very largo bodies, much exceeding the sun in magnitude, and having that mysterious faculty they possess of rushing up towards the sun, passing close around him, and then vanishing never to return (or returning after a period calculated to a nicety as in the case of the recent return of Halley’s famous comet—M.P.). It is a strange faot that these large bodies are closely associated with meteors, which in many instances are so small in dimensions a child could easily handle them. THE COMET’S COURSE EXPLAINED BY GRAVITY.

Comets come from outer space, and after travelling almost directly towards the sun for a long period of time, they circle around him, and pass away again into the depths of space. There is a fact which seems at first to remove them from all the ordinary laws of motion, but it was precisely that fact that first gave astronomers a proof of the truth regarding the law of gravity. Newton took the comet of 1860, and having found that it was travelling on a parabolic course—better described as an exceedingly long oval —was able to say that the comet would follow such and such a course, although ite orbit was of an entirely different nature from the planets, \nd continually changing in appearance day by day. Yet he said: “1 will follow that body and tell precisely where it will go.” It was this mastery of the laws of celestial motion by Newton that first convinced astronomers of the truth of the law of gravity. The comet came and followed tho precise path that Newton suggested. Let us see how the comet moved. It came travelling up towards the sun, seeming to move directly toward him, marked among all comets by the directness of its path towards the sun. When it was within a sixth part of the sun’s diameter, it circled around him and then passed away on a track precisely like that on which it had arrived. Like all other comets of distinction it had a long tail, and as it approached the sun, that tail extended, according to the known laws of comets, away from the sun, and was thus carried behind the oomet. As the comet passed around the sun—this was accomplished in a few hours—it was seen on the other side adorned with a long tail 90,000,000 miles in extent, the tail being no longer behind the comet, but travelling in front of it. In the day or two that the comet was lost eight of, that long tail was thrown out as it retreated from the neighbourhood of tho sun. Now that comet had taken four weeks in approaching tho sun over a distance of 90,000,000 miles, though having at starting, all tho velocity with whioh it had arrived, but in less than four days that wondrous tail, 90,000,000 miles long, was thrown out in front of the body. Tliore is a fact which either shows us that we have to deal as to a comet’s tail with matter which has not been formed in reality, but is in some way made to become apparent to us, or else wo have to deal with a repulsive forco. This repulsive fore© of the sun seems incomparably greater than that of gravity. (‘Nowadays,” according to Hinks, of Cambridge Observatory, “one can speak with some confidence of the part which the pressure of light may play in the formation of comets’ tails. Light pressure would account for the fact that the comet’s tail is’ always turned away from the sun, the powerful source of light. As the comet approaches, the tail streams behind; as the comet recedes, the tail goes before; so that evidently the source of repulsion lies in the sun.”) HALLEY’S COMET. „ Norton assigned a path to the comet ot 1680, but was not able to predict its period. Meanwhile, his friend Halley occupied himself applying the new theory of gravitation to calculating the orbits of comets. He argued, if' a comet returned again and again to the sun, at must be to all intents am purposes a planet; and if so, why might it not be expected to perform its revolution around the sun at a regular period. Allowing for the disturbances caused by tho massive planets Jupiter and Saturn, as the comet passed them on the way, Halley blamed them for causing irregularities in the time of the comet’s return. A comet is lighter and sensitive to disturbance, easily captured and easily turned adrift, so .that the attractions of the planets might account for thendelay.

Taking the comet of 1682 as an example, Halley found the period of seventy-four years eleven months, at one return, and seventy-six years two months at another. By making allowances for disturbances caused by the planets, he ventured to predict the return of the comet in 1758. He knew that' he could never live to see the prediction verified, but he expressed himself content with the faith that impartial posterity would not refuse to admit that this was first discovered by an Englishman. THE COMET’S RETURN IN 1759. When 1759 came, astronomers went over the calculations made by Halley, and they found from their greater mathematical experience how that comet might be dealt with. They were able to tell the very month and even predict the day. They said upon April 13, 1759, with a limit of error of one month, this comet would come back to its point of nearest approach to the sun. It actually returned and made its nearest approach t-o the sun on March 13, 1759, or just within the limits of error. They did not know at the time that the planets Uranus and Neptune existed, so no allowance had been made for their influence on the comet.

But when the year 1835 was approaching, astronomers had learned about Uranus, though Neptune had not been discovered, and also how to deal much more perfectly with the processes of mathematical analysis involved in calculating the course of celestial bodies, and they said that the comet would return in November, 1835, and they put the dates between November 12 and November 16. A German astronomer, Roseiiberger, gave the exact date as November 13, and the exact date on which the comet did hiake its nearest approach to the .mi was November 12. As it approached the sun it presented a very emarkable head, with a crescentic idge of brightness. It seemed as if it were forced from ;ide to side by some disturbing force xerted by the sun. The comet passed '.round the sun, made its nearest approach and came around on the other side, passing southward. Thou it was

observed by astronomers of the southern hemisphere, who found that the comet, instead of presenting the appearance it had when it approached the sun, now appeared not only without a tail but without a head. It looked like a small bright speck, and nothing distinguished it from a star, exoept that it was moving slowly over the n eayens. As days passed on it increased in size, and seemed to be trying to develop a tail, but failed in the attempt. It was noticed that there seemed to be a power in the sun to raise from the nucleus of the comet vaporous mater, which was again swept away by the sun. Sir John Herschel, at that time, said that in his opinion that was the nature of the economy of a comet. The sun not only has power to raise the matter, but to repel it as well. EVIDENCES OF THE REPULSION THEORY. lou notice I am dwelling on that fact of repulsion. I want to show that power of tho sun in repelling matter. I will now deal with a small comet, which has a very curious history. We have here all tho evidence we can get, though it is not very striking. In the year 1770, a small comet made its appearance. It was watched for a time, and was found not to be travelling in a long oval path like that of Halley’s comet, but in a path which was completed within a period of five and a naif years. It W’as called Loxell, after the name of the astronomer who detected it first. It was never seen again, and astronomers were then led to inquire: “ What has become of the comet?” Tracing back its path, they found it had travelled so near to Jupiter that the giant power of that planet arrested it in its course, sending it away on an entirely different path from that on which it had travelled before. Search for it was useless, since it was now hopelessly lost. The question then arose, “ How was it that this comet of very striking appearance had never been seen before.” Travelling in a period of five and a half years, why had it so far escaped attention Astronomers traced it back and calculated its path, and they found that the same giant hand which sent the comet away was responsible for its temporary capture. In 1667, it was found that the comet approached quite near to Jupiter, so close in fact as to intrude itself among the satellites of Jupiter. Jupiter is not the planet to stand any nonsense of that sort, and so compelled it to follow another course. ■ Another five and a half yeans, and another like peiod, and it was then seized by Jupiter, and sent outside the solar system, and where it has gone nobody knows. There is a rather curious fact in connection with the French revolution. Blangui, a republican, was imErisoned, and he took it into his ead to write about comets, and something made him look on Jupiter as a sort of policeman, whom he described as always patrolling on the watch for comets. When they came near ho drove them into the perilous straits, and it was well for the comets if they could escape from that time forth. _ (A number of comets are row recognised and spoken of, as Jupiter’s "family” of comets, of which twentyseven are reckoned at present.—M.P.) LEXELL’S COMET. To return to Lexell’s comet '. It had gone into the midst of Jupiter’s satellites. They are not large objects, and if the oomet had any mass he could disturb them; but instead of that, all those satellites are still traversing the path they had before the comet arrived, and we\ learn, therefore, that that comet at any rate was mere vapour. It had no power and no weight, although it was much larger even than Jupiter. It was unable to disturb those little satellites which Jupiter manages so easily. BIELA’S COMET. I now pass to a description cf a comet which appeared in 1826, concerning which some curious facts were revealed. It was known as Biela’s comet, after the name of an Austrian officer who first detected it among the stars. It was found on examination of the Herschal records, that it had been seen before by Catharine Herschel and others, and a path wns assigned to it tf six years and eight months. Now the comet was remarkable in the first place because its path actuallv crossed the oarth’s path; and, indeed, on the next return in 1832, astronomers announced that the comet would cross the earth’s path. Great alarm was caused, as many feared this.meant a collision. A member of the Paris Academy said it was imprudent for astronomers to make such an announcement, for in 1771 announcements made in that way drove people insane. In 1832 the people were very much frightened, and they had to be reassured. They were tolrl that the mere fact of the comet passing across the path of tho earth would not interfere with the earth, nor would it injure the path which wns not a material thing. Nevertheless, the people were frightened, fearing that astronomers had not calculated the path of the comet so exactly as- to be assured no collision would result with the earth. Nothing happened, however, the comet coming and going without causing any disastrous results.

When it returned in 1846, the comet was found to be travelling along its usual path, but to the great surprise' of astronomers the comet divided into two, each part having a distinct head and nucleus. The comets travelled along, side by side, for more than four months, at an almost unvarying distance of about 160,000 miles, without showing the least sign of mutual attraction or disturbance. Internally, however, both comets were intensely active, each developing a bright nucleus, and a tail some half a degree in length, and at times the two comets were connected by a faint are of light. At their next return in August, 1852, they were both seen., now separated by about 1,500,000 miles, and travelling quietly along tlieir appointed paths. Neither of theip has ever been seen since that date, although they ought to have returned five times, eo they apparently vanished. FINAL CHAPTER IN HISTORY OF COMET. However, in 1872, when the comets or rather fragments were again due, on the night of November 27, just as the earth was passing the old track of the lost comet, a wonderful meteoric shower took place. (It seemed as though Biela’s comet wos shedding over us the fragments now scattered along its path, a like display taking place in November 1885, and 1892, when the earth once more passed the comet’s path.—M.P.)

CONNECTION OF METEORS WITH COMETS. I pass from the subject of comets, wonderful as they are, to meteors. For a long time meteors were looked upon as phenomena of our atmosphere, but facts began to be observed which led to a different conclusion. One fact was that well-defined showers could be looked for on certain dates. Take for instance the shower of November 27. What could it mean P Why should a shower of meteors take place on that date, or any special dav. as far as the earth was concerned? Nevertheless, on November 27, when the earth is passing through a particular part of her course, she is saluted by certain missiles which strike the atmosphere from without* and become illuminated in passing through it. (Since the particular part of her course through which the earth is passing coincides with that in which Biela’s comet formerly crossed this path, the inference is that the meteor showers encountered at regular intervals on November 27 are undoubtedly composed of the debris of that comet,

the view now generally accepted by astronomers. This special display is referred to as tho Bielids or Andromedes, since they come from the direction of the constellation Andromeda. It occurs once in about thirteen years. -M.P.) THE LEONID SHOWERS.

Tho finest star shower ever recorded seems to have taken place in 1833, and an observer declared that "lie never saw snow-flakes thicker in a storm than were the meteors in the sky, at some moments.” Not a sound * was heard, nor were any particles known to reach the earth. (The display was repeated in 1866, but that of 1899 was extremely disappointing, to judge from world-wide reports, and personal observations.—M.P.

The Leonids so-called, since they come from the direction of the constellation Leo, are due once in thirty-three years, and always! appear on or about November 15. However, the meteor swarm is stretched out along the path to, such a distance, that the procession is nearly three years in passing any given point. The researches of Professor Newton, of New Haven, U.S.A., and Adams who discovered Neptune, led to the astounding discovery that meteors travel in the track of oomots, and that the two are intimately connected. A comet which appeared in 1866, known as Temple’s comet, was found to be travelling along a path practically identical with that of the Leonids. The August meteors or Perseids, were moving in the same path as that of the bright comet of 1862, known as Tuttle’s comet. Finally no doubt remained as to a connection between, the meteoric shower of the Andromedes in 1872, now following in the track of Biela’s comet. (More than one hundred meteor-swarms are now recognised, and Professor Alexander Herschel found four or five others, which have a 11 comet annexed,” so to speak.—M.P.) METEORS. But this seems too immense. These objects a few grains in weight, travelling along regular paths, returning at regular intervals, yet subject like the giant planets to the controlling law- of gravity which keeps them from wandering indefinitely beyond the , domain of their mighty ruler the Sun. ‘‘Pelted by star-dust, stoned by meteor falls,” the earth pursues its journey around the sun, tho meteoric downfall adding yearly to its mass. The rate at which the meteoric particles penetrate the atmosphere surrounding our planet is very much more rapid than tnat of a bullet. Were it not for the protecting atmosphere surrounding our planet, we should oertainly lie destroyed. . However, when a meteor encounters the atmosphere, its velocity is reduced, and then it is consumed through the heat which is generated, and finally falls earthward in the form of vaporous dust. On the tops of mountains, the material forming these meteors have been found.

Space then is filled with flying fragments, either thrown out from the volcanoes of the moon, in the days of its youth, or ejected from the distant stars, but whatever their origin, the -resemblance between them and elements to be found in the earth show after all, that

‘‘We are but part of one stupendous whole, Whose bodv Nature is, and God the • Soul.”