298 Notices respecting New Books. 



subtending an angle of 4", and never quite so well-defined as to give 

 a positive assurance of the existence of a solid sphere — much less 

 could any phase at any time be discerned on it. The whole was 

 encircled with a strong coma which nearly filled the field of view 

 (15" diameter), dying away insensibly but rapidly at the edges. 

 When the nucleus was brought to any part of the circumference of 

 the field, the border of the coma fell little short of the centre. On 

 the south preceding side, however, its extent was somewhat greater, 

 projecting in that quarter into a feeble and irregular appendage, 

 which might be regarded as a rudimentary tail." — P. 397. 



The changes which the comet underwent in its figure and dimen- 

 sions, as also in respect of the relative degrees of illumination of its 

 different parts, were extremely remarkable, and are of great import- 

 ance in reference to the study of its physical constitution. On the 

 25th of January some measures were taken with the equatorial. 

 The diameter of the head in declination was found to be 237"'3 ; 

 and upon the measure being repeated about two hours and a quarter 

 after it was found to be 252" , 0, or about 14"' 7 greater. Such a 

 difference in so short an interval of time, and in opposition to the 

 tendency of the morning twilight, " seemed inconceivable, and threw 

 a momentary doubt on the exactness of the earlier observation. 

 That measure had, however, been taken and read off with all possible 

 care, and in short nothing remained but the conclusion, that the 

 change was real, and that the comet was actually increasing in dimen- 

 sions with such rapidity that it might almost be said to be seen to groiol 



" On the next night, the 26th, the increase of dimension of the 

 comet was evident at the first glance. Its form, too, had undergone 

 a change, being more elongated in pi'oportion in the direction of its 



axis, and materially less definite in its posterior region The 



coma had also undergone a great and remarkable change, not so 

 much in dimension as in brightness ; being very much enfeebled. . . . 

 The head or envelope had begun to assume an evident tendency to 

 a paraboloidal form, the posterior portion being terminated, however, 

 by an outline of an oval or nearly semicircular figure. The nucleus 

 appeared as a star about the 11th magnitude, not, however, sharp 

 and sparkling like a true star, but furred and nebulous, so that, with 

 its ray, it presented exactly the appearance of a miniature comet, 

 having a head and tail of its own." — P. 399. 



On the 27th of January, the head or envelope, with its enclosed 

 nucleus or ray, was still more dilated than on the preceding night, 

 but the coma was grown extremely thin and faint. On the 2Sth 

 the coma wa3 all but gone, but there were long irregular nebulous 

 tails in various directions. The nucleus was no longer a dim misty 

 speck but a brilliant point. The observations of this night conclude 

 with the following memorandum : — " so ended a most memorable 

 night. I can hardly doubt that the comet was fairly evaporated in 

 perihelio by the heat, and resolved into transparent vapour, and is 

 now in process of rapid condensation and re-precipitation on the 

 nucleus." 



The 29th and 30th proved cloudy. On the 31st the comet was 



