April 1, 1887.] 



♦ KNOW^LEDGE ♦ 



135 



THE NEW COMETS.* 



By Richard A. Pkoctor. 



LEEADY the year 1887 has three comets 

 on its record, one of which promises to be 

 conspicuous. Small comets, indeed, are 

 found to be so common that we must expect 

 soon to hear of cheaper rates than ai-e at 

 present proffered, somewhat to the lower- 

 ing of cometic dignity, for theii' discovery. 

 When prizes were first offered for comet- 

 finding, the value of the prize ran, unless I mistake, to 100^. 

 Now, ten or twenty comets may be discovered for less 

 money, and what was thought fair work for a year is now 

 accomplished in less than a month. 



The discovery that comets of the smaller type are so 

 numerous is, however, important in itself, though none of 

 the small comets recently discovered have presented any 

 features of interest. Whatever theory is eventually 

 accepted respecting comets must give an account of then- 

 great numbers, and it will be found that this is a criterion 

 of no slight significance. Combined with what has ah-eady 

 been discovered regarding comets and meteors (the kinsfolk 

 of comets), this discovery goes far in my opinion to indicate 

 the true origin and meaning of these interesting bodies. 



The trouble about comets and meteors of late has been 

 that the students of astronomy seem unable to keep count 

 at one and the same time of all the known facts. They 

 insist on starting theories which will account excellently for 

 this or that fact, but are manifestly inconsistent with other 

 facts as well established. 



Thus Schiaparelli, noting that some comets have orbits 

 passing near the orbits of one or other of the giant planets, 

 suggests that the giant planets have from time to time cap- 

 tured comets or meteor systems which, before that last 

 unfortunate visit of theirs to our solar system when Jupiter 

 or Saturn or Uranus or Neptune captured them, had been 

 wandering about unattached to any system through inter- 

 stellar space. The theory le;ives far the larger number of 

 comets and meteor systems unaccounted for, it gives no real 

 account even of the origin of those which exhibit the pecu- 

 liarity it strives to explain, and, as a matter of fact, the 

 giant planets have been proved to be quite incapable of 

 playing the part assigned to them. But for these defects 

 the theory would perhaps be acceptable enough. 



Again, Prof. Newton, of Yale, noting that meteor 

 streams ti'avel in the tracks of comets, advances the theory 

 that meteors have been, as it were, chipped oft' from comets. 

 But as meteors present peculiarities of structure by no 

 means explained by this theory, a-s a comet must exist 

 before meteors can be chipped from it, and as the cluppLng 

 process is mechanically impossible, this theory also is open 

 to some slight objections. 



Then again, Tscliermak, noting the resemblance of struc- 

 ture between meteorites and volcanic products suggests that 

 meteoi-s of all orders (which would include meteor streams, 

 and therefore comets) were shot out from the earth in 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 

 never come witliin many millions of miles of the earth's 

 orbit, 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, deduced 

 from the microscopic structure of certiiin meteorites the 

 startling theory that they had once been inside the sun ; for 

 there is evidence that their substance once existed in the 



* Reprinted from the -Vtvc lurk H'orld, 



form of globules of molten metal, which aggregated into 

 large masses, which in turn were exposed to violent friction, 

 indicating conflicting motions at very high velocities. 

 " W^here else," wrote Sorby, in 1864, " could such conditions 

 exist, except fii-st in the interior, and afterwards in the 

 immediate neighbourhood of our sun ? " But it is absolutely 

 certain that the theory as thus suggested cannot possibly be 

 true, either as a general explanation of meteoi's and comets, 

 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 sunborn, and subsequently dis- 

 turbed by planetary attractions so as not to return to 

 their parent orb. A flight of meteors, shot out from the 

 sun, as Sorby suggested, might have velocity enough to get 

 away from him for ever, in which case we should never see 

 a ti-ace of it again, not 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 grazing by past the 

 sun's surface. (The comets of 1843, 1880, and 1882, which 

 all had the same orbits 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.)* As a 

 general theory, this fails like the others. 



Better, though still failing as a general theory, is that 

 suggested by Graham, of London, to account for the large 

 quantitie,s of hydrogen " occluded " within the substance of 

 certain iron meteoi-s, and by Daubree, the French physicist, 

 to account for the volcanic structure of meteorites. 

 According to theii- theory, meteors, and therefore comets, 

 were shot forth from the interior of stars. As Graham put 

 it, " the iron meteors have brought to us, across the inter- 

 stellar depths, the hydrogen of the fixed stars." And 

 Daubree, by ari-anging meteorites into their several orders, 

 and showing how volcanic products may be similarly 

 arranged in a series including all the forms found in 

 meteorites, extended the theory of stellar origin to include 

 all orders of meteors. Yet are there fatal objections against 

 this, at any rate, as a general theoiy. It leaves unexplained 

 the peculiai'ity which Schiaparelli had tried to interpret — 

 the strange tendency among certain comets to hang about 

 the orbits of the giant planets. Moreover, now that the 

 meteor streams crossing our earth's track are numbered by 

 hundreds, a theory which explained all meteoi-s as sprung 

 from the stars woidd indicate an inconceivably immense 

 number of meteor sti-eams within oui" solar system to 

 account for our earth's track crossing so many. 



To get at the true general theory of comets and meteors 

 we must combine what is sound in all these theories, since 

 the true theory must accord with all the known facts. This 

 is what the theory I have maintained during the past few 

 years actually does, and that is why, so far from admitting 

 that it is a daring theory, I regard the others as overbold 

 (running " a travers " known facts, as they all do) and 

 mine as cautious and modest, startling though its fimdamental 

 idea may seem. 



All comets and meteors, according to my theory, are sun- 

 born. But it is not to om- own sun, with Sorby, nor to 

 those other suns, the stars, with Graham and Daubree, 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 teirestrial astronomers. Millions of 



* Since this appeared it has been announced that the new comet 

 discovered in the Southern skies is also following in the same track — 

 confirming my theory that the comets of 1668, 1813, 1880, and 18S2, 

 were parts of 'one large comet, dissipated, doubtless, millions of 

 years ago. 



