280 The Great Comet ^1861. 



discussed without requiring inofe labour than can be, at present, 

 devoted to them. 



Within the last few days the principal ray in the part near the 

 nucleus, has assumed a more regular sweep in the direction op- 

 posed to that of the diffuse tail, which now reaches nearly to the 

 centre of Corona Borealis, scarcely changing the course of its 

 southern limit between x and t Bootis and t, Coronae Borealis from 

 night to night. 



The telescopic phenomena, though interesting, have not present- 

 ed equally strongly defined features with those which characterized 

 the great comet of 1858. We should perhaps except from this 

 remark their structure for a day or two after their first emission 

 from the nucleus. In this stage they were intersected by jets of 

 luminous matter projected from the nucleus, and these limits were 

 pretty clearly outlined. 



On the 2d, portions of three were visible ; the inner one show- 

 ing a variety of details. In its outline and general aspect it was, 

 like others which followed it, almost a fac simile on an enlarged 

 scale of some of those exhibited by the great comet of 1858. 

 They rapidly faded, or were lost in the surrounding haze and 

 their places were filled by new ones. Latterly, two, at most, could 

 be seen at one time. It is quite important to remark that the 

 successive envelopes resembled their predecessors not only in their 

 general aspect but quite closely in the details of their structure ; the 

 luminous jets not issuing at random from all points alike of the 

 nucleus, but continuing to follow a nearly similar course at each 

 new discharge from its surface. 



The most natural inference from this would seem to be that the 

 nucleus, if it rotates at all upon an axis, does so very slowly. Of 

 the pendulum-like vibrations of the luminous sectors ascribed by 

 Bessel to the comet of Halley, nothing was seen ; although the 

 opportunity of witnessing them, had they existed, was very favor- 

 able, as the sectors were well displayed. 



The nucleus was throughout brilliant, and, to appearance, solid, 

 with a diameter of from 2" to 3". 



The disposition of the nebulosity in the part of the tail conti- 

 guous to the head was nearly uniform throughout ; the axial dark- 

 ness being scarcely distinguishable, excepting on one occasion, 

 July 3d. 



The following positions have been derived from comparisons 

 with neighbouring stars. 



