HALLEY'S COMET.

Otago Witness, Issue 2928, 27 April 1910, Page 65

HALLEY'S COMET.

IS THERE ANY DANGER? By J. F. Morris, Sen. When Halley's Comet wa,3 picked up by the camera in 1909 it- was more than 300 millions of miles away from the sun. On December 1,1909, it was in opposition but. was too faint to be seen with small the wanderer being only equal to a star of about the twelfth magnitude. It continued to approach the earth ixntil ; December 18, 1909, when ita distance from us would be about 125 million? of miles. During January and February, 1910, it receded from us (its motion is retrograde), and increased its distance from the earth. In March it crossed the earth's orbit at a point which our earth will pass about the time of our Southern Vernal Equinox (September. 23). Its distance then would be (March 24) about two radii of the orbit —that is, 180 million of miles, the earth being then a* on-3 end of the orbital diameter and the comet at the - other. About the middle of April it will be in our eastern sky. It was reported as having been seen at Gore on April 9. On April 20 Halley's Comet will be in perihelion, according to Mr John Grigg, F.R.A.S., of the Thames, and, to miote his words, "will probably be an object grand, impressive, and brilliant." Then our visitor rushes along its parabolic course, still coming towards the earth. It passes between us and the sun about May 17, and a few days later comes very near us from a sidereal point of view. Although it is said to come very near us, it will be still 12 millions of miles distant. At this time the comet should be easily observable in the early evening, and, in all probability, still be an. impressive and thought-promoting object. In a few days more our celestial visitor will double its distance from us; later still it will gradually dimmish in apparent size and briqhtness. till it fades from view altogether, not to appear again until 1987. This last must be taken for what it is worth, and is my first attempt in that line. Now, as to the question. " Is there any danger from a comet?" the improbability of any danger from such a source has been frequently pointed' out. Thie celestial wanderer is supposed to menace a large segment of our sphere, because the hul crosses our orbit on or about May 18. Moreover. M. Camille Flammarion, who, I need hardly eay, is one of the most noted and laborious astronomers of the present day, is erroneoual-v credited with countenancing this improbability. In M. Flammarion's - book, "Astronomy for Women," English translation ("Astronomy for Amateurs." page 201), he j alludes to the danger which might happen j " if one of these orbs were to arrive j directly upon us." On page 202. et seq, he goes on to speak of such a contingency as not only improbable, but "as an almost impossibility." The Ju'visy astronomer finishes off the whole argument for and against with the following sentence : " So we may sleep! in peace as regards future danger likelv to come to us from comets. There is little fear of the destruc- , tion of humanity-by these balls of wind." This book I have referred to is procurable in Dunedin. is very cheap, and ought to be in the Carnegie Library. -^ It will be remembered by a good few of j

, those who take more than a passing in- ' terest in the harmonics of the Sidereal Movements that the late Mr Proctw was accused of saying that the comet of 1881 Would cause the destruction of the earth. j In his book, " Mysteries of Time and Space," be devotes a whole " chapter to repudiating and ridiculing such a con' elusion. In the present case, the words "arrive directly" have a peculiar and : scientific signification to the student of the mechanics governing the collision of bodies in motion, with which I need not bother the reader; suffice it to say that there is nothing in physics to warrant j the assumption that tbe earth and a ' comet would be likely to collide, j Chemistry also seems to point to the same conclusion as regards the so-called "comet's tail." Even supposing that the " tail " is gaseous, and supposing further that these gases were poisonous, yet, as Professor Turner points out, '' only one ' part in 100,000 parts of air will be of the same chemical element as the tail of the comet." Another eminent scientist, Professor A. Fowler, of the Royal College of Science, South Kensington, also throws some light on the subject under discussion. In addition to the remarks he made, which were recently published, I may further be allowed to quota from his intensely interesting lecture. After alluding to the intersection-of the comet's I tail with the earth's orbit, the learned j Professor goes on to say: —That would be a very interesting event. He did no Jknow precisely what would happen, bu* some people thought we should all be • suffocated by the gases of which the tail : was composed. He did not think it would I be so dreadful as that. In their own j laboratories lately they had discovered the nature of the gases which composed the tail, and those of them who were I interested in ' astrophysics were rather anxious to run the risk for the sake of the knowledge they would be able to gain. It was quite likely, however, that they would witness a display of aurora. —Conclusion. — With all the great master minds in the intellectual world of science who make a special study of astro physics there seems to me a general- concensus of opinion i against the chances of collision among the cometary bodies. Neither does there seem to be the least probability of a collision between a planet and a comet. If the planet were as big as Jupiter, for instance, and as far removed from the sun, that planet, in my opinion, would begin to attract it when within 60 or .70 radii of the planet. The planet would then impart its own velocity to the comet, still attracting it, and, turning the comet's tangential velocity to account, would alter the comet's parabolic or hyperbolic curve to a more or less parallel curve to the | planet's curve—that is, a concentric circle whose centre of gravity would be the centre of the planet. In other words, it I would turn the comet into a satellite ! whose primary would be the planet. But our earth is nothing like the mass of Jupiter, and, moreover, is too near the sun, therefore the attractive force of the earth on the comet is infinitely small, while on the other hand the force of the sun is infinitely great on the comet's mass.. At its nearest approach to the earth, if my figures are right, it will be travelling with a velocity of 2,160,000 miles per day. During all that distance on the curve its inclination towards the earth is so infinitely little that the moon, our next-door neighbour, has 250,000 chances against one of the comet's of giving us a bump. In any case the earth is too small and the sun is too massive' at the given distance of the centre of gravitation—namely, the sun's centre distance, 92,897,000 miles—for the earth to attract any celestial body 12 million miles away. Therefore the only reasonable deduction we can arrive at its this : , that, seeing the sun is the great centre j of attraction of our solar system, such : attraction imtvarts greater velocity to any in motion is towards the centre of attraction ; the inclination of all bodies i in motion to lean towards the centre of gravity; the greater the velocity the ! greater the "heel over." Taking these things all into consideration, we can arrive j at no other deduction than that the sun i has complete , control oyer all celestial '■ bodies that are menibei\3 of or visitors to ; our solar system. He is master in his own house and grounds. All must obev. One sentence more, and I have done. When the j Great Master Mind of the universe I planned out infinite snace. when He called to His aid those wonderful and stupendous j

forces of Nature of which we know only a few, there was one formulated l and ap? plied to the astro mechanics of our system at any rate, and that was gravitation as piled to the astro mechanics of our system, Moreover, . He enunciated the following decree, which became a law: —These bodies,. these orbs of the universe; these stars, these planets, everything which has motion, voluntary or applied, even man, and everything in motion which, man himself can apply motion to, shall be subject to a force, passing through the body's centre of gravity, constant in magnitude, and always , directed . towards (as.. far as we ar© concerned) the centre of the circle. The centre of the circle in this case is the sun, which is also the centre of the force. The comet leans over towards the sun as it rushes along with awful velocity on its parabolic curve, prior to getting its send-off to the uttermost limits beyond Neptune, to appear again, if I may make so bold, in the year 1987. .