Scr. XXXVI. HALLEY'S COMET. 343 



orbit. In the one position the sun will seem to be four 

 times larger than he appears to us, and at the other he 

 will not be apparently larger than a star (N. 221). 



On the first appearance of Halley's comet, early in 

 August, 1835, it seemed to be merely a globular mass of 

 dim vapor, without a tail. A concentration of light, a 

 little on one side of the center, increased as the comet 

 approached the sun and earth, and latterly looked so 

 like the disc of a small planet, that it might have been 

 mistaken for a solid nucleus. M. Struve, however, saw 

 a central occultation of a star of the ninth magnitude by 

 the comet, at Dorpat, on the 29th of September. The 

 star remained constantly visible, without any considera- 

 ble diminution of light ; and instead of being eclipsed, 

 the nucleus of the comet disappeared at the moment of 

 conjunction from the brilliancy of the star. The tail 

 increased as the comet approached its perihelion, and 

 shortly before it was lost in the sun's rays, it was between 

 thirty and forty degrees in length. 



According to the observations of M. Valz, of Nismes, 

 the nebulosity increased in magnitude as it approached 

 the sun ; but no other comet on record has exhibited 

 such sudden and unaccountable changes of aspect. The 

 nucleus, clear and well defined, like the disc of a planet, 

 was observed on one occasion to become obscure and en- 

 larged hi the course of a few hours. But by far the 

 most remarkable circumstance was the sudden appear- 

 ance of certain luminous brushes or sectors, diverging 

 from the center of the nucleus through the nebulosity. 

 M. Struve describes the nucleus of the comet, in the 

 beginning of October, as elliptical, and like a burning 

 coal, out of which there issued, in a direction nearly op- 

 posite to the tail, a divergent flame, varying in intensity, 

 form, and direction, appearing occasionally even double, 

 and suggesting the idea of luminous gas bursting from 

 the nucleus. On one occasion M. Arago saw three of 

 these divergent flames on the side opposite the tail, rising 

 through the nebulosity, which they greatly exceeded in 

 brilliancy : after the comet had passed its perihelion, it 

 acquired another of these luminous fans, which was ob- 

 served by Sir John Herschel at the Cape of Good Hope. 

 Hevelius describes an appearance precisely similar. 



