10 Observations on Donati's Comet. 



First appearance of Comet to the naked eye, at 6h. 45m. 54s. 

 p.m., Melbourne mean time ; altitude, 17° 24'. 



Fig. II. — Eleven minutes later; the tail, or rather as it 

 now appeared, the wings were more visible, and I observed a 

 very peculiar pulsation in the luminous matter gathered 

 round the nucleus and forming the wings. Suddenly the 

 wings were extended (as shown in Fig. II.), where the 

 dark space between the wings is seen to come almost close 

 up to the nucleus ; as suddenly the wings were retracted, or 

 sheathed up (as shown in Fig. III.), where they are short- 

 ened, and the luminous matter connects them together for a 

 great distance from the nucleus. When the wings were re- 

 tracted they appeared less distinct. The time required to 

 produce these effects was only one second, half of which was 

 occupied by the light leaving the neighbourhood of the nu- 

 cleus, the other half in returning to the same. Fig. II. re- 

 presents the head of Comet and part of the tail, or the wings, 

 as seen when the pulsating light has gone forth at 6h. 56m.. 

 54s., while 



Fig. III. represents Comet and tail, or wings, half a second 

 later, viz., 6h. 56m. 54s-5., with the same light brought 

 home again. This playing of the luminous matter was most 

 distinctly visible to the naked eye, and reminded one of the 

 up -rising rays of light during an aurora, with this difference, 

 that the pulsation, apparently in the Comet, was infinitely 

 swifter. The space traversed during one-half of a second was 

 from one-third to one-half of the whole length of the tail. 

 This phenomenon, after several irregular intervals, lasted 

 till the Comet, later in the evening, appeared in full brilliancy, 

 about half-way between the point where it was first visible 

 after sunset, and the horizon. This phenomenon was most 

 distinct when it commenced, and was gradually lost in the 

 full light of the Comet. 



Fig. IV.— The Comet in its fullest light at about 7h. 37m. 

 Nucleus of an oval shape, more convex on that part which 

 faces the sun, less so on the opposite side ; of a dull, pale- 

 yellowish color; apparent diameter of nucleus, about one- 

 fourth of the diameter of Venus. In front of nucleus, and 

 touching the same, is a band of light, which, turning round 

 on each side and backwards, enters the tail. In front of that 

 band of light is a less defined and less intense layer of lumi- 



