1867.J Astronomy. 381 



has been satisfactorily subjected to spectrum-analysis. Mr. Huggins 

 found that the nucleus was gaseous, and that the coma was either 

 composed of (finely divided) matter in a state of incandescence, or 

 shone by reflected light. The comet had no visible tail. 



Signor Schiaparelli had before noticed that if we suppose the 

 August meteors to describe a very eccentric orbit (as their great 

 velocity entitles us to do), the elements of their orbit, calculated 

 from the observed position of their radiant point, agree very closely 

 with those of the orbit of Comet II., 1862. The following table 

 exhibits the resemblance between the orbits : — 





August Meteors. 



Comet II., 1862. 



Perihelion distance 



0-9643 . 



0-9626 



Inclination 



. 64° 3' . 



. 66° 25' 



Longitude of perihelion 



343° 28' . 



. 344° 41' 



Longitude of node 



. 138° 16' . 



. 137° 27' 



Direction of motion 



Retrograde 



Retrograde. 



The period of this comet, which it will be remembered was a 

 large and in other respects remarkable one, has been calculated by 

 Dr. Oppolzer to be about 142 years, and the orbit extends into 

 space far beyond that of Neptune. 



Dr. Edmund Weise, of Vienna, has pointed out the coincidence 

 of many other observed meteor-tracks with cometic orbits. We 

 conclude the discussion of this interesting subject with his sketch of 

 the process by which the whole orbit of a comet is conceived to be 

 strewn with meteoric bodies, not following each other in one path, 

 but dispersed many thousands, perhaps many millions, of miles on 

 every side of the central track. If we consider, he says, the circum- 

 stances under which a comet approaches the sun, we shall see that 

 individual particles must be repelled to a distance where, " collect- 

 ing under the original laws of aggregation around new centres ol 

 gravity, they will revolve about the sun in orbits closely resembling 

 that of the parent-comet. In the case of periodical comets, these 

 dispersed aggregations will gradually collect along the whole orbit, 

 and if the comet's orbit intersect, or approach very near to the 

 earth's orbit, the phenomenon of periodic showers will be produced 

 at the annual passage of the earth through the point of inter- 

 section." 



Mr. Stone has detected a small error in Leverrier's deter- 

 mination of the Solar Parallax. The error lies in the numerical 

 work. Leverrier's method is (in theory at least) very beautiful, 

 and is little known. The earth has an orbital motion around the 

 common centre of gravity of the moon and earth ; the diameter of 

 this orbit being about 6,000 miles. In Leverrier's method the 

 earth's motion in this small orbit is taken advantage of to deter- 

 mine the sun's distance. The size of this subsidiary orbit being 

 determined from the estimated mass of the moon, and the dis- 

 placement of the sun due to the earth's excursions in her monthly 



