THE BIRTH AND LIFE OF COMETS.

New Zealand Mail, Issue 772, 17 December 1886, Page 7

THE BIRTH AND LIFE OF COMETS.

Cornhill Magazine,

If an orb like the sun ejects from its interior the materials for forming a first-class comet, it must send forth that flight of meteors in good style, or else the cometic progeny will return to the bosom of its solar parent * like the prodigious son ’ —as Liuncelot has it—a disappointment and a failure. The ejected matter must start forth at the rate of a few hundreds of miles per seeoud. In our sun s case 380 miles per second would suffice. A noteworthy effort must be nude, even by such a giant as a sun, to effect this lively ejection. But that a sun is capable of it, no one who considers the might of our sun can for a moment question. He is 325,000 times as strong as this little earth on which we live. His vitality is shown by his lustre, which is about equal to the light which would come from two millions of millions of electric burners. It is shown also by his tremendous emission of heat, equal to what would result from burning each second a mass of coal (of the best quality be it understood) 200 miles broad, 200 miles long, and 200 miles high—that is, eight million cubic miles of coal. This would be about 12,000 millions of millions ot tons per second (the whole output of our exceptionally coal-producing country is but about 150 millions of tons per annum). The sun, then, and doubtless every one of his fellow suns, the stars, has undoubtedly the requisite power, if only it had the will to eject matter in the required manner. Now, of course, our own sun is not often engaged upon such work as this. Although most active and vigorous, the source, indeed (directly or indirectly), of aIL life and energy within his system, he works steadily, not fitfully. Yet every now and then he spurts into sudden though local activity of the most amazing kind. In one of these fits he shot out a flight of bodies whose swift motion through the hvdrogen atmosphere which enwraps the sun was measured at 200 miles per second, and indicated (a* was shown by mathematical computation) a velocity of 450 miles per second, as the missiles left the sun’s surface. Since tnetime (1872) when the sun was first caught in the act of thus' ejecting matter away from, his own interior for ever (because he caa never bring back matter which leaves him w*th a velocity of more than 380 mile 3 pecj second) he has been detected four or five times at the same lively business. Theret can be no doubt, then, either about the smass power to eject matter from his interior as tfn»" giant planets and our own earth seem, tohave done, or about his exerting that power from time to time. And what_the sua_ca.it; do his fellow-sun 3 can do likewise. In fact, ju?t as our earth is a sample planet, so the sun is a sample star. Now supposing there are 10,000 millions of stars in our galaxy—a most moderate calculation—that each one ot

them has been in the sun-like state for ten

millions of years (our earth actually tells us by her crust that the sun has been at work as now for 100 millions of years), and that in. ten years on the average only one ejection such as we are considering has taken place, then there would be 10,000,000,000,000,000 star-ejected meteor flights or comets travelling about the interstellar spaces. With so goodly a probable supply we need not wonder if our solar system is from time to time visited by larger comets, such as these ejections might be supposed to have given birth to in the past. But a few of the comets which from time to time visit our sun may be regarded as his own children returned to him—not to stay, only to pay a sort of flying visit. The greater number of the comets ejected by him and returning -'"'for want of sufficient velocity at starting—“to their old home, would come straight to the warm bosom of their parent, and there rest

Absorbed in never-ending glory In the heart of the great ruling sun. But although this would be the usual end of such bodies, and though those paradoxers err who imagine that bodies shot out from the sun could ever circle around him as the planets do, yet it might easily happen that one of these returning comets might miss its aim, if we may so speak. Very moderate perturbation, such as the giant planets are well able to produce, would so affect the movements of the comet that on its return to the sun it would steer clear of the globe, and go back into the depths from which io had returned. In the case of those large comets, like Newton’s in 1680, and the comets of 1665, 1843, 1880, and 1882, whose -orbits pass very near to the sun’s globe, we may fairly imagine this to be the true inter* pretation. We should in that case have this interesting result—that while the sun, by his over-mastering attraction, prevents these comets which were expelled by the giant planets from passing out of the solar system, the giant planets have in some cases prevented these comets which were expelled (hundreds of thousands of years, probably, ago) by the sun from returning to his parent orb, and have so compelled them to remain members of his family. If the comet families of the giant planets are now chiefly ruled by the sun, those comet children of the sun which still belong to the solar family owe their position partly to the giant planets. The perplexity with which astronomers have viewed the comets of 1665, 1843, 18S0, and ; 1882 may be partly removed by this explanation of the origin of all these bodies. What made them so mysterious was that they travel on paths which near the sun, are practically identical; so that, until the close of 1882, the idea was commonly entertained that they were one and the same body which had come back, after gradually diminishing circuits, in 1843, after 178 years’ absence* in 1880 after 37 years’ absence, and in 1882 after only 2£ years’ absence, and might be expected to return in a few months, and perhaps to lash the surface of the sun to intense splendor and heat, destroying thereby all life within the solar system. But the comet of 1882 passed away on such a path that it could be well watched, and we know now certainly that it will not return for several hundreds of years. Now if we suppose that long, long ago the sun shot out a flight of meteors forming presently a comet, which afterwards came to travel on a path passing very close, almost grazingly, by the sun s globe, we see that this comet might very well at one of its returns be broken up by the sun’s action, as Biela’s comet actually was broken up in 1845. Very slight differences in the velocities of these comets, when near the sun, would cause differences of several years in their periods of circuit. One of the comet fragments came back, if this explanation is right, in 1665, another in 184-3, another in 1880, and yet another in 1882. There may be more yet to come.