THE GREAT COMET OF 1858. 



07 



V. 



Discussion of the Observations of the Great Comet of 1858, with the Object of deter- 



mining the most probable Orbit 



By G. W. HILL. 



by T. H. Safe 



The interesting physical aspect of this comet attracted the attention of astron- 

 omers to it in an unusual degree, a large part of which was expended in 

 obtaining observations for position. Consequently, we have a large mass of 

 material for determining its orbit, not a little of which is of very good quality. 

 Added to this, the quite long period of the apparition of the comet (nine 

 months), would enable us to obtain the elements with considerable precision. 

 Moreover, hints were thrown out that some other force besides gravity might 

 enect its motion. Although these seem to have had no foundation other than 

 the tact that the orbits derived from three normals did not well represent 



the intermediate observations, yet it is a matter of some interest to clear up 

 the suspicion. 



As the first step in the work, I determined to reduce the observations to 

 uniformity, in respect to the places adopted for the comparison stars; which 

 last I proposed to derive from all the material accessible to me. The desir- 

 ableness of this course is evident when we consider that the observers at Bonn, 

 Kremsmunster, Ann Arbor, and the two observatories in the southern hemis- 

 phere reobserved their comparison stars, in consequence of which their obser- 

 vations agree much better among themselves; while the rest contented them- 

 selves with places from Lalande, BessePs Zones, or the British Association 

 Catalogue, and their results exhibit larger probable errors. And as the comet 

 w as observed nearly simultaneously in Europe, the same comparison star was 

 frequently used by a dozen observatories for the same night's work ; and thus 

 tn e stars of the latter class of observatories mentioned above are often found 

 anu >ng those reobserved by the former. The result of this labor has convinced 



