COMET AND ITS TAIL.

Dominion, Volume 3, Issue 821, 19 May 1910, Page 8

COMET AND ITS TAIL.

f ,> ' & j> DR. KENNEDY'S LECTURE. WHAT TO EXPECT TO-NIGHT. fHO DANGER, BUT PERHAPS A 'y-' BRILLIANT SCENE. . The intenso interest which Wellington people 'are taking in tho visit of ; Halley's Comet was demonstrated by the presence of a crowded audience in ■ the Concert Chamber at tho Town Hall last night, when tho Rev. Dr. Kennedy, "A.S., delivered a lecture en' the jjeet.. Extra chairs were brought *nd placed in every available foot of spaoe, and even then many listeners remained standing, and a very large number were unable to gain admission The Mayor (Mr. T. M. Wilford, M.P.) presided, and among those present were: The Ven. Archdeacon Devoy, tho ; Hon. G. Fowlds, .the Hon. Dr. Findlay, and many leading citizens. The lecture was heard throughout with the closest attention, and the speaker's pleasant manner and gift of luminous exposition enabled hiiii to make even the abstruse portions of his subject - . delightful in the hearing. Why It Is' Interesting. . The lecturer said the comet was particularly interesting through its history and its association with tho great scientist, Edmund Halley; and also through its present brilliant appearance in the heavens; and, further, owing to its anticipated transit across the sun's disc to-day, and the subsequent passage of the earth through the comet's tail'. The same beautiful, brilliant object had been observed by ancient peoples and generations ■ that had passed away more than two thousand years ago. Of Edi mund Halley, whose name the comet bore, it had been said that if one of the stars was displaced, he would immediately detect the accident. The i lecturer. spoke of the career of Halley, j and alluded to his important scientific achievements, beginning with his>schooldays. Newton had already discovered the great law of universal gravitation, under which every particle of matter in the universe was attracted by every other in inverse proportion to tile square of the distance between them, and also in direct proportion to their magnitude. , ; The Path of the Comet. The lights were then turned down, and a series of lantern slides were shown, beginning with a portrait of ■ Halley, the discoverer not of the comet, but of the fact of its periodicity; • The slides that immediately followed were used to .explain the character of the "'parabola, and the lecturer went on to explain Newton's theory that the orbits of comets were parabolas. Halley made use of' this theory, persuaded Newton to work ont anew the results • ho had lost, and enabled him to publish his immortal "Principia." The law of- » universal gravitation was the key to all theoretical and mathematical astronomy,' and the world owed this key to two great English scientists, Isaac Newton, who discovered it, and Edward Halley, who generously published it to the world.

Halley Only Saw It Once. It was not known who discovered Bailey's . Comet. Halley himself probably only saw it once, and then imperfectly, owing to a cloudy sky.' In the course of • his researches Halley found that a comet or comets had appeared at Tegular intervals of 75 years. He ascertained that the orbit in each instance was nearly the same, and he then concluded that the appearances were ■ all of ono comet, and predicted that it ■would return in 1758. Ho afterwaids altered this to early in 1759, so as to allow for the comet being delayed by . the attraction of certain of the planets. •" This prediction was exactly verified by tho return of tho comet 16 years after Halley's death. Most of the comets appeared once, and never returned, and Halley's was the'first whose periodicity was ascertained. Cerman' Astronomer's Honour. One picture showed the photograph . ©f Halley's Comet taken last September by Max Wolfe, tho German astronomer. This had been regarded as the first photograph of the comet on its present visit, but it had since been . identified on. a photographic- plate taken in Egypt. Max Wolfe was, however, tho. first to recognise the planet on it-a present visit. The comet's previous appearances had been traced back to 240 years before Christ, when a comet, supposed to bo Halley's, was recorded by the Chinese. Twenty-nine appearances of tho comet f were named on a. chart displayed by the lecturer, and these included its ap- . pearanco at the time of the Norman Conquest, 1066. The lecturer showed by -means of the lantern a section of the Bayeux tapestry, with a rude representation of tho comet, a group of Englishmen pointing at it, and King Harold receiving the news of it, and, as tho lecturer remarked, "already tottering on his throne." Above was the inscription in the imperfect Latin of the day: "Isti miraut stella'." The next important appearance was in 1656, soon after the t-aking of Constantinople, and when the Christians were still warring against thd Turks. Comet.Photographed at Meeanee. Many pictures of astronomical apparatus were shown, and also many reproductions of pictures of Halley's and othqr coinuts made at different poriods and showing in some instances the contrast between the apparently imaginative drawings of earlier days, and tho accurate photographs- produced with tho aid of modern appliances. A particularly interesting series showed ilalley's comet as photographed on Boveral recent oceasionh at the Meeanee observator). Some of the slides had been made more graphic by putting in & representation of the sun, so as to show the position the comet will occupy in relation to tho sun this morning, and afterwards. Tho process of photographing the comet wa-s also explained, and tho apparatus used for the purpose at Meeanee was graphically represented. With the aid of diagrams, the orbit of the comet was shown in relation to the solar system, and its Varying rates of movement—rapid when near perihelion (going round the sun) and much slower before and after aphelion (at its greatest distance from the sun}. .

Transit Across the Sun To-day. A particularly interesting chart allowed the path of Halley's Comet amongst the stars, and in this connection the lecturer said that after the transit, we should probably not set it again until May 21, when it would be a prominent, evening object. Exact as was the knowledge of astronomers as'to the movements of comets— ns for instance, it was known thai the comet would begin its transit across tho sun at 1.02 p.m. to-day, and would be in transit exactly one hour—there was still much to be learnt about their composition arid iheir light, especially that portion of their light which was not borrowed from the sun. The size of the solid particles in the comet was unknown. Some said tho.v were no larger than pins' heads, and were hundreds of feet apart, each one being surrounded by glowing gas. Tliei« must be some solid particles', bccause, if the comet consisted solely of gas, it

would not keep together, but would bo dissipated in space. Anotnor strango tiling was the repelling action of tho sun upon the tail of a comet, so that while tho comet generally was..drawn towards tho sun, tho matter forming V'o tail shot out and curved over, and tell away like the spray of a fountain. The tail of a comet was often hollow. Tho different shapes taken by comets' tails were clearly shown and classified. Marvels of the Spectroscope. Tho spectroscope, its uses and somo of its results, were also explained with the aid of. the lantern, and special reference was mado to the ascertainment thereby of the fact that the tail of tho comet consists of some gas—probably one of tho hydrocarbons at a very low pressure—so low indeed that even if it consisted of a poisonous gas like cyanogen, it would be so rarefield that it ,might be breathed without any ill effects. The action of the spectro-lieliograyili was also shown, tho lecturer expressing tho view that it was only by means of this instrument that any representation of tho comet's transit across tho sun was likely to be obtained. Cannot Hurt Us. Tho reason why the ordinary photographic processes would probably be unavailing was that the comet was too attenuated to obscure tho rays of the sun. ' "We can find nothing on the earth," said the lecturer, "to compare it with except Nothing. It- is 100,000 times less dense, than the air around us." 1 The lecturer did not anticipate any success , for the projected endeavour of some, aeronauts to bottle'up some of the comet's tail. If wo passed through the comet's head, one might have a shower of aerolites, but we should not pass through its head., either on the present occasion or at its next visit — if ever. We should not get nearer than 14 million miles of tlie head this time. A picture taken from a magazine, and showing St. Paul's Cathedral in flames and ruins as the supposed effect of the comet was tho text for an exposure by the lecturer of a mass incorrecthistory ajid pretended science. Another picture showed a brilliant meteor shower, and this, the lecturer said, was what we might possibly see to-night. The atmosphere of the earth would be quite sufficient' to make a great hole through the tail. It would protect us like a coat of mail; not only from poisonous gases, but also from any missiles of.the solid matter of. the comet. , Applause, which had frequently been heard during - the lecture, broke out loudly at the close, and testified to the great' appreciation of the lecture. A vote of thanks was carried by acclamation. ' The. chairman announced that Dr. Kennedy would repeat his lecture tonight, so that the large number of people who were crowded out would have an opportunity of hearing it. THE COMET IN VERSE. A RHYME FOR .ASTRONOMERS. The following verses were recited by the Rev. Dr. Kennedy in the course of his lecture last evening:—

Of all the meteors in the sky There's none like Comet Halley; We see it with the naked 1 eye, And periodically; ' The first to see it was not he, But still we call it Halley; The notion that it would return Was his originally. Of all the years we've lately seen There's none to rival this year; Because, though busy we, have been We're likely to be busier. When five and seventy years have sped, Then back conies Comet Halley; Harold us that it would return, ; ,, A'nd mathematically." > Some probe the secrets of the sun, And most effectually; There's much good honest work being done Solenographically.. Whatever quest may prove the best, We all admire bold Halley, Who said his coiuet would returnPerhaps perpetually. TRANSIT ACROSS THE SUN'S DISC. In connection with tho transit of Halley's comet across the sun's disc; to-morrow between 1.50 and 2.50. p.m., it is estimated that the comet will enter the sun on the side towards the west, traverse the disc almost across the centre and leave on tho > eastern edge. Yesterday a small sun-spot was present near the western limb, a moder-ate-sized spot near the middle; and a large double spot closely followed by about five minute spots about twothirds from the eastern edge of, the sun towards the middle. There is not likely to be much alteration in these spots tomorrow and they may serve as a guide when observing the transit of tho comet. VISIBLE FOR SOME TWO OR THREE WEEKS. (By Telegraph.—Press Aesoclutton.i Auckland, May 18. Professor Seagar, interviewed this afternoon, said that, to-morrow morning an exceptionally fine view of the tail of Halley's comet would be visible provided that the weather oonditions are favourable. The head, or nucleus, will not be visible, however, as it rises at about tho same time as tho sun. We shall be passing through the tail during to-morrow afternoon or evening, and it is possible .tSiat part of it will be visible in the western sky to-morrow night after twilight. Professor Seagar says there should be a fine view of tho comet in tho western sky on tho following evening just above the horizon. It will be visible to the naked eye for some two or three weeks to come and will £et fainter and fainter. Tho moon will interfero to some extent with its luminosity and it will be hardly as bright an object as it has been in tho morning sky.

"EARTH WON'T PASS THROUGH TAIL" Regarding Halley's Comet, Mr. Beattie, a Sydney .astronomer, writing to the Sydney "Daily Telegraph," says: It has been stated by astronomers both here and in England that if the tail is long enough we shall probably pass through it oil May IS), but' 'I think I can show that, although the length of the tail 'is amply sufficient, it is not at all likely that we shall pass through it. The conditions for such an event postulate not that the nucleus shall pass the iine of nodes simultaneously with the earth, us is the case, but that the section ot the tail situated 15 million miles from the nucleus shall do so. In order that this should happen in the present case, it would be necessary for the axis of the tail to lie almost exactly on the radius vector, which would mean that the ejected particles roust traverse the 15 million miles in a few minutes, ivbicb wo know is impossible. Assuming a possible rate of ejectment of 10,000 miles per minute, or about six t times the comet's orbital motion at the time, the tail would then be inclined at, about 9J degrees to the radius vector, and the section ?.t earth's distance would be about li million miles from the line ol nodes. Tl\is distance would take 25 hours to traverse, and during that interval the earth itself will have sped along in its orbit more than H million miles- in an opposite direction. As the orbit of the comet is inclined at an angle of about 18 degrees, with the plane of the it follows that tho earth will pass by the south side of the tail at about five-sixths of its visible length from the nucleus, and at a distance from its edge which will be greater or less according (is the tail is found to bo .inclined at a greater or i less angle with tlie radius vector.