220 Appearance of Comet II. at Pans. 



APPEARANCE OF COMET II. AT PARIS. 



NOTE FKOM M. CHACOKNAC. 



The second comet of this year, now visible near the Pole, pre- 

 sented to view, on the morning of the 10th and 11th of August, 

 a luminous aigrette, analogous to that which was observed in 

 Halley's Comet at the time of its last appearance. The sector 

 was much more brilliant than the rest of the nebulosity, and 

 turned towards the sun. Its amplitude was forty-six degrees 

 at three on the morning of the 10th; on the 11th, at ten 

 minutes past two in the morning, the amplitude proved to be 

 sixty-five degrees. Thus this sector widened, like that of 

 Bailey's Comet, as the nucleus approached the sun. 



Besides this alteration, which might be compared to the 

 expansion of the corolla of a convolvolus, the eastern branch of 

 the sector which, on the morning of the 10th, was the most ex- 

 tended and brilliant, and which measured an arc of forty-five 

 seconds, exhibited only a rudimentary form on the morning of 

 the 11th. The western ray, on the contrary, became developed, 

 and subtended an angle of sixty-three seconds, and its bright- 

 ness surpassed that of the eastern ray. 



On the 10th, the nucleus presented the aspect of a fusee 

 ("d'une fusee"), that is to say, it had a much longer diameter 

 in the direction of the radius vector than in that of the perpen- 

 dicular. The proportion of these two diameters was as one to 

 three. I had not hitherto observed the nuclei of comets to be 

 lengthened in this direction. The great comet of 1858, and 

 that of 1861, both exhibited the contrary phenomenon; the 

 lesser diameter of their nuclei were towards the direction of 

 the radius vector. 



On the 11th, this aspect had much diminished, and the two 

 diameters of the comet's nucleus approached equality. No 

 certain trace of polarized light was visible in the nucleus ; and 

 still less could it be detected in the light of the sector. 



In short, the appearance of luminous expansion in the 

 form of an aigrette directed towards the sun, presented by 

 Halley's Comet, and which had already been observed, by 

 Heinsius in the head of the comet of 1744, are not exceptions 

 peculiar to the nature of those comets. The great comet of 

 1858, that of 1861, and even the last comet of short period 

 which has appeared, have presented luminous expansions, 

 which I have observed, and which may be compared to a 

 vaporous jet directed towards the sun, and forced to retreat by 

 an action emanating from that luminary. 



This comet, which now presents to the eye a brilliancy equal 

 to that of a star of the fifth magnitude, and may be expected 



