174 



SCIENCE. 



[Vol. YIII., No. 185 



regarded as of the same nature as the star-shower 

 meteor, for no one now seriously claims that the 

 comets are fragments of a broken planet. The 

 hypothesis of the existence of such a planet is it- 

 self arbitrary ; and it is not easy to understand 

 how any mass that has become collected by the 

 action of gravity, and of other known forces, 

 should, by internal forces, be broken in pieces and 

 these pieces sent asunder. The disruption of such 

 a planet by internal forces, after it has by cooling 

 lost largely its original energy, would be specially 

 diflficult to explain. 



We cannot, then, look to the moon, nor to the 

 earth, nor to the sun, nor to any of the large 

 planets, nor to a broken planet, as the first home 

 of the meteoroids, without seeing serious if not 

 insuperable objections. But since some of them 

 were in time past certainly connected with comets, 

 and since we can draw no line separating shoot- 

 ing-stars from stone-meteors, it is most natural to 

 assume that all of them are of a cometary origin. 

 Are there any insuperable objections that have 

 been urged against the hypothesis that all of the 

 meteoroids are of like nature with the conaets, 

 that they are in fact fragments of comets, or it 

 may be sometimes minute comets themselves ? If 

 such objections exist, they ought evidently to 

 come mainly from the mineralogists, and from 

 what they find in the internal structure of the 

 meteorites. Astronomy has not as yet furnished 

 any objections. It seems strange that comets 

 break in pieces, but astronomers admit it, for it is 

 an observed fact. It is strange that groups of 

 these small bodies should run before and follow 

 after comets along their paths, but astronomers 

 admit it as fact in the case of at least four 

 comets. Astronomically, there would seem to be 

 no more difficulty in giving such origin to the 

 sporadic meteor, and to the large fire-ball, and to 

 the stone-meteor, than there is in giving it to the 

 meteor of the star-shower. If, then, the cometic 

 origin of meteorites is inadmissible, the objections 

 must come mainly from the nature and structure 

 of the meteoric stones and irons. Can the comet 

 in its life and history furnish the varied conditions 

 and forces necessary to the manufacture or growth 

 of these peculiar structures ? 



It is not necessary, in order to answer this ques- 

 tion, to solve the thousand puzzling problems that 

 can be raised about the origin and the behavior of 

 comets. Comets exist in our system, and have 

 their own peculiar development, whatever be our 

 theories about them. It will be enough for my 

 present purpose to assume as probably true the 

 usual hypothesis that they were first condensed 

 from nebulous matter ; that that matter may have 

 been either the outer portions of the original solar 



nebula, or matter entirely independent of our 

 system and scattered through space. In either 

 case, the comet is generally supposed, and prob- 

 ably must be supposed, to have become aggre- 

 gated far away from the sim. This aggregation 

 was not into one large body, to be afterwards 

 broken up by disruption or by solar action. The 

 varieties of location of the cometic orbits seem in- 

 explicable upon any such hypothesis. Separate 

 centres of condensation are to be supposed, but 

 they are not a priori unreasonable. This is the 

 rule rather than the exception everywhere in 

 nature. 



Assume, then, such a separate original conden- 

 sation of the comet in the cold of space, and that 

 the comet had a very small mass compared with 

 the mass of the planets. Add to this the comet's 

 subsequent known history, as we are seeing it in 

 the heavens. Have we therein known forces and 

 changes and conditions of such intensity and vari- 

 ety as the internal structure of the meteorites 

 calls for? What that structure is, and, to some 

 extent, what conditions must have existed at the 

 time and place of its first formation, and during 

 its subsequent transformations, mineralogists 

 rather than astronomers must tell us. For a long 

 time it was accepted without hesitation that these 

 bodies required great heat for their first consoUda- 

 tion. Their resemblance to the earth's volcanic rocks 

 was insisted on by mineralogists. Prof. J. Law- 

 rence Smith, in 1855, asserted without reserve that 

 "they have aU been subject to a more or less 

 prolonged igneous action corresponding to that of 

 terrestrial volcanoes." Director Haidinger, in 

 1861, said, " with our present knowledge of natural 

 laws, these characteristically crystalline forma- 

 tions could not possibly have come into existence 

 except under the action of high temperature com- 

 bined with powerful pressure." The likeness of 

 these stones to the deeper igneous rocks of the 

 earth, as shown by the experiments of M. Dau- 

 bree, strengthened this conviction. Mr. Sorby, in 

 1877, said, "it appears to me that the conditions 

 under "which meteorites w^ere formed must have 

 been such that the temperature was high enough 

 to fuse stony masses into glass : that the particles 

 could exist independently one of the other in an 

 incandescent atmosphere subject to violent me- 

 chanical disturbances ; that the force of gravita- 

 tion was great enough to collect these fine jjarticles 

 together into solid masses, and that these were in 

 such a situation that they could be metamorphosed, 

 further broken up into fragments, and again col- 

 lected together.' 



Now, if meteorites could come into being only 

 in a heated place, then the body in which they 

 were formed ought, it would seem, to have been a 



