Contributions to Astro-Meteorology. 45 



of the larger planets, its orbit will be changed, and may become 

 one of short period, like those of certain comets. If, moreover, 

 its perihelion distance is less than the distance at which solar 

 attraction disintegrates the groups, the cloud is dissolved into 

 independent particles. Diversity of planetary perturbations 

 produces in the orbits of these particles a variety of elements, 

 especially variety in the periodic times. The group is gradually 

 lengthened along the ellipse, and after a certain number of re- 

 volutions the cloud becomes a continuous ring. The meteors of 

 November belong to such a group while the ring is partially 

 formed. The August meteors probably represent a group after 

 it is transferred into a continuous ring. 



M. Schiaparelli gives a summary of the consequences which 

 result from the preceding discussions in the following proposi- 

 tions, which establish the basis for a new theory of falling stars. 



I. Matter is disseminated in celestial space in all possible grades 

 of division. The first grade consists of the larger stars, either iso- 

 lated or collected in systems of few members. The second is made 

 up of large agglomerations of small stars (the star dust of Herschel), 

 into which many nebulae are seen to be resolved by large telescopes. 

 Then follow smaller bodies, which are invisible except when they ap- 

 proach the sun under the form of comets. Finally, the last grade 

 consists of cosmical clouds composed of very minute elements, which 

 have a weight comparable to that of objects which we are accustomed 

 to handle or transport on the earth. 



" II. This last class of bodies may have been formed in space by 

 the local concentration of the celestial matter in a manner analogous 

 to the crystallization of substances chemically dissolved in liquids. 

 From what occurs in these crystallizations we are even led to think 

 that such a form of aggregation is much more probable and more 

 frequent than the others, which take place by large masses. Hence 

 the volume occupied by the cosmical clouds may be a notable fraction 

 of the stellar space. 



" III. The movements of such clouds among the bodies of the 

 universe are comparable to those of the fixed stars, and are probably 

 due to analogous causes. When any one of them enters the sphere 

 of attraction of the sun, it cannot be visible to us unless its orbit 

 relative to this great luminary is a very greatly elongated conic 

 section. 



" IV. Whatever may be the form and extent of a cosmical cloud, 

 it cannot (with very rare exceptions) penetrate to the interior of the 

 solar system unless it has been transformed into a parabolic current, 

 which may consume years, centuries, and myriads of years in passing, 

 part by part, its perihelion, forming in space a river whose transverse 

 dimensions are very small with respect to its length. Of such cur- 

 rents, those which are encountered by the earth in its annual motion 

 are rendered visible to us under the form of showers of meteors di- 

 verging from a certain radiant. 



