DONATI S COMET. 487 



centre appeared to separate it into two luminous portions. On the 

 2nd October the coma round the head had become broader, while the 

 nucleus had become brighter. On the 15th the tail, though much 

 fainter and diminished in magnitude, appeared broader and of a more 

 hyperboHc form than before, and the nucleus which was round and 

 pretty well defined on the side away from the sun, exhibited a brighter 

 and more irregular appearance, with flame-hke jets, in that portion 

 which was turned towards it. 



"The following approximate places were obtained at 7 p. m, on the 

 13th and 14th September : 



Right Ascension. Declination North. 



13th llh 12' 35" 36° 32' 



14th llh 18' 24" 36^ 33' 



From the l3th to the 20th the variation both in Right Ascension 

 and DecUnation was slow. The following are the places more recently 

 observed, and which may be taken as very nearly correct : 

 p. M. Right Ascension. Decline. 



Sept. 20, 7:00 llh 48' 56"... ......36° 20' N. 



" 24, " 12h 6' 8" 35° 10' 



" 25, " 12h 24' 39"... ......34° 34' 30" 



Oct. . 2, " 13h 36' 36" 26° 10' 



" 5, 6:50 14h 12' 50".. 19° 3' 



" 14, 6:31 15h 58' 10" 10° 44' S. 



" 15,6:1147' 16h 8' 28" 13° 48' 



" 18, 6:14 30' 16h 37' 25" 21° 51' 



The observations were made in the Observatory here with the 

 large equatorially mounted telescope constructed by Mr. Alvan Clarke, 

 the object-glass of which has 6^ inches of aperture, and of which the 

 Right Ascension reads to four seconds of time, and the Declination 

 Circle to one minute of arc. 



The motion of the Comet is, as will be seen from the above, retro- 

 grade. The elements of its orbit have not yet been given, so far as we 

 have observed, either in Britain or here : and although three observa- 

 tions, taken at short intervals, are theoretically sufficient for their 

 determination, some time must elapse, and the whole series of observa- 

 tions will require to be taken into consideration before they be fully 

 ascertained, and their accordance with the observed places verified. 

 We know, however, by simple trigonometrical calculation, its nearest 

 distances from the sun and earth, and thence, by micrometrical and 



