ASTRO-METEOROLOGY. 337 



in I860 so astonished the Scientific world, afforded decided indica- 

 tions of its presence. 



Dr. Weiss, of Vienna, regards comets as the original bodies by 

 whose disintegration meteor - streams are gradually formed. 1 In 

 this respect his views differ somewhat from those of Schiaparelli. 2 

 " Cosmical clouds," he remarks, " undoubtedly appear in the universe, 

 but only of such density that in most cases they possess sufficient 

 coherence to withstand the destructive operation of the sun's attrac- 

 tion, not only up to the boundaries of our solar system, but even with- 

 in it. Such cosmical clouds will always appear to us as comets when 

 they pass near enough to the earth to become visible. Approaching 

 the sun, the comet undergoes great physical changes, which finally 

 affect the stability of its structure : it can no longer hold together : 

 parts of it take independent orbits around the sun, having great 

 resemblance to the orbit of the parent comet. With periodical com- 

 ets, this process is repeated at each successive approach to the sun. 

 Gradually the products of disintegration are distributed along the 

 comet's orbit, and if the earth's orbit cuts this,' the phenomenon of 

 shooting-stars is produced." 



The characteristics of the different meteor-streams afford interest- 

 ing indications in regard to their relative age, the composition and 

 magnitude of their corpuscles, etc. etc. Thus, if we compare the 

 streams of August 10th and November 14th, we shall find that the 

 latter probably entered our system at a comparatively recent epoch. 

 We have seen that at each return to perihelion the meteoric cluster is 

 extended over a greater arc of its orbit. Now, Tuttle's comet and the 

 August meteors undoubtedly constituted a single cluster previous to 

 their entering the solar domain. It is evident, however, from the 

 annual return of the shower during the last 90 years, that the ring is 

 at present nearly if not quite continuous. That the meteoric mass had 

 completed many revolutions before the ninth century of our era is 

 manifest from the frequent showers observed between the years 811 

 and 841. At the same time, the long interval of 83 years between 

 the last observed display in the ninth century, and the first in the 

 tenth, indicates the existence of a wide chasm in the ring no more than 

 1,000 years since. 



The fact that the meteors of the November stream are diffused 

 around only a small portion of their path, seems to justify the conclu- 

 sion that the transformation of their orbit occurred at a date compara- 

 tively recent. Leverrier has calculated that the meteoric cloud passed 

 very near Uranus about a. d. 126. He regards it, therefore, as highly 

 probable that this was its first approach to the centre of our system. 3 



1 Astronomische JVachrichten, Nos. 1710, 1711. 



5 For a condensed statement of SehiapareuYa theory, see an interesting article by 

 Prof. Newton, in Sillimaii's Journal for May, 1867. 3 Comptes Bendus, lxiv., p. 94. 



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