176 



SCIENCE. 



[V^OL. V^III,, No. 185 



full of all the scenes and actions required for the 

 growth of such strange bodies as have come down 

 to us. Some of our meteors, those of the star- 

 showers, have certainly had that history. What 

 good reason is there for saying that all of tliem 

 .may not have had the like birthplace and life? 



The pieces which come into our air in any recur- 

 ring star-shower belong to a group whose shape is 

 only partly known. It is thin, for we traverse it 

 in a short time. It is not a uniform ring, for it is 

 not annual, except possibly the August sprinkle. 

 How the sun's unequal attraction for the parts of 

 a group acts as a dispersive force to draw it out 

 into a stream, those most beautiful and most fruit- 

 full discussions of Signor Schiaparelli have shown. 

 The groups that we meet are certainly in the shape 

 of thin streams. 



It has been assumed, that the cometic fragments 

 go continuously away from the parent mass, so as to 

 form, in due time, a ring-like stream of varying den- 

 sity, but stretched along the entire elliptic orbit of 

 the comet. The epochs of the Leonid star-showers 

 in November, which have been coming at intervals 

 of thirty-three years since the year 902, have led 

 us to believe that this departure of the fragments 

 from Tempel's comet (1866, I.) and the fonnation 

 of the ring was a very slow process. The meteors 

 which we met near 1866 were therefore thought 

 to have left the comet many thousands of years 

 ago. The extension of the group was presumed 

 to go on in the future until, perhaps tens of thou- 

 sands of years hence, the earth was to meet the 

 stream every year. Whatever may be the case 

 with Tempel's comet and its meteors, this slow 

 development is not found to be true for the frag- 

 ments of Biela's comet. It is quite certain that 

 the meteors of the splendid displays of 1872 and 

 1885 left the immediate vicinity of that comet later 

 than 1840, although at the time of those showers 

 they had becoTne separated two hundred millions 

 of miles from the computed place of the comet. 

 The process, then, has been an exceedingly rapid 

 one, requiring, if continued at the same rate, only 

 a small part of a millennium for the completion of 

 an entire ring, if a ring is to be a future form of 

 the group. 



It may be thought reasonable in view of this 

 fact about Biela's comet, established by star- 

 showers of 1872 and 1885, to revise our conception 

 of the process of disintegration of Tempel's comet 

 also. The more brilliant of the star-showers from 

 this comet have always occurred very near the end 

 of the thirty- three year period. Instead of there 

 being a slow process which is ultimately to pro- 

 duce a ring along the orbit of the comet, it cer- 

 tainly seems more reasonable to suppose that the 

 compact lines of meteors which we met in 1866, 



1867, and 1868 left the comet at a recent date. A 

 thoiisand years ago this shower occurred in the 

 middle of October. By the precession of the 

 equinoxes and the action of the planets the shower 

 has moved to the middle of November. One-half of 

 this motion is due to the precession, the other half 

 to the perturbing action of the planets. Did the 

 planets act upon the comet before the meteoroids 

 left it, or upon the meteoroid stream ? Until one 

 has reduced the forces to numerical values, he 

 may not give to this, question a positive answer. 

 But I strongly suspect that computations of the 

 forces will show that the perturbations of Jupiter 

 and Saturn upon that group of meteoroids hun- 

 dreds of millions of miles in length, — perturbations 

 strong enough to change the node of the orbit 

 fifteen degrees along the ecliptic, — would not 

 leave the group such a compact train as we found 

 it in 1866. If this result is at all possible, it is 

 because the total action is scattered over so many 

 centuries. But it seems more probable that the 

 fragments are parting more rapidly from the 

 comet than we have assumed, and that, long 

 before the complete ring is formed, the gi'oups 

 become so scattered that we do not recognize 

 them, or else are turned away so as not to cross 

 the earth's oi'bit. 



Comets, by their strange behavior and wondrous 

 trains, have given to timid and superstitious men 

 more apprehensions than have any other heavenly 

 bodies. They have been the occasion of an im- 

 mense amount of vague and wild and valueless 

 speculation by men who knew a very little science. 

 They have furnished a hundred as yet unanswered 

 problems whicli have puzzled the wisest. A 

 world without water, with a strange and variable 

 envelope which takes the place of an atmosphere, 

 a world that travels repeatedly out into the cold 

 and back to the sun, and slowly goes to pieces in 

 the repeated process, has conditions so strange to 

 our experience, and so impossible to reproduce by 

 experiment, that our physics cannot as yet explain 

 it. But we may confidently look forward to the 

 answer of many of these problems in the future. 

 Of those strange bodies, the comets, we shall have 

 far greater means of study than of any other bodies 

 in the heavens. The comets alone give us speci- 

 mens to handle and analyze. Comets may be 

 studied, like the planets, by the use of the tele- 

 scope, the polariscope, and the spectroscope. The 

 utmost refinements of physical astronomy may be 

 applied to both. But the cometary worlds will be 

 also compelled , through these meteorite fragments, 

 — with their included gases and peculiar minerals, 

 — to give up some additional secrets of their own 

 life, and of the physics of space, to the blowpipe, 

 the microscope, the test-tube, and the crucible. 



