48 



REPOKT 1871. 



as forming, in some cases, distinct meteor-systems or families of radiant- 

 points, of which the principal, occurring in the first half of the year, may be 

 grouped as follows : — 



Families or groups of Radiant-points. 



Should the effect of planetary perturbations, which retarded the retiirn of 

 Halley's comet in the year 1859 nearly one month from the time of its perihelion 

 passage, as calculated by D'Alembert and Clairault, also explain the wide differ- 

 ence between the separate coils of spiral meteoric streams apparently encoun- 

 tered by the earth in the meteor-systems of which the above groups or families 

 of radiant-points appear to present unmistakable examples, a new field of 

 investigation in meteoric astronomy, and of future observation and reseai'ch, 

 is beginning to unfold itself in these new and interesting discoveries. 



2. On Comets and Meteors, by Professor Kirkwood, Indiana University, 

 U.S. (read before the American Philosophical Society, November 19, 1869). 

 In an able treatise on " Meteoric Astronomy," already noticed in these 

 Eeports (for 1868, p. 418), a short Appendix (B) at the end of the volume 

 on " Comets and Meteors " expresses the views on their connexion which 

 Professor Kirkwood communicated, so long ago as Jidy 1861, to the ' Danville 

 Quarterly Review' for December in that year. "Different views are enter- 

 tained by astronomers in regard to the origin of comets, some believing them 

 to enter the solar system ah extra, others supposing them to have originated 

 ■within its limits. The former is the hypothesis of Laplace, and is regarded 



with favour by many eminent astronomers Now, according to 



Laplace's hypothesis, patches of nebulous matter have been left nearly in 

 equilibrium in the interstellar spaces. As the si;n in his progress ap- 

 proaches such clusters, they must, by virtue of his attraction, move towards 

 the centre of our system, the nearer portions with greater velocity than the 

 more remote. The nebulous fragments thus drawn into our system would 

 constitute comets ; those of the same cluster would enter the solar domain at 

 periods not very distant from each other. ... If we adopt Laplace's hy- 

 pothesis of the origin of comets, we may suppose an almost continuous fall of 

 primitive nebular matter toward the centre of our system — the drops of 

 which, penetrating the earth's atmosphere, produce sj)oradic meteors, the 

 larger aggregations forming comets. The disturbing influence of the planets 



