181 



SCENERY OP THE HEAVENS. 



comet. A notice of it occurs as early as the commencement of the tenth century. The 

 first telescopic view was obtained by Simon Marius, loth December 1612, who compared it 

 to a candle shining through a horn ; that is, a diluted light, increasing in density towards 



Nebula in Andromeda. 



a centre. This nebula is of lenticular shape, and forms nearly a right-angled triangle with 

 Almaach and Mirac, the two principal stars of Andromeda. A good eye may pick it up 

 on a favourable night, by projecting a line from Sheratan, the second star in Aries, through 

 Mirac, to about 4^ beyond. It is about half a degree long, and from 15' to 20' broad. 

 Herschel believed this to be one of the nearest nebulae in the heavens, though at a 

 distance two thousand times greater than that of Sirius. Notwithstanding the improved 

 optical means of the moderns, it has not been resolved into stars, though no doubt can be 

 entertained of its stellar composition. Numerous telescopic stars appear involved in the 

 glow, but are not supposed to have any connection with it, being interposed between it 

 a,nd our system. 



There are examples of nebulse presenting circular or slightly oval disks, resembling 

 planets, but with different degrees of definition at the borders. In several instances they 

 appear of " a fine and full blue colour, verging upon green." They are no doubt clusters 

 of stars reduced by mutual proximity and vast distance to the form of planetary disks. 

 Sometimes they are found combined in pairs, like the physically connected double stars ; 



Planetary and Double Nebula*. 



and if they are to be regarded as two distinct star-systems, each having its own centre of 

 condensation, yet revolving round each other by the tie of gravitation, the imagination can 

 scarcely realise the vastness of the idea suggested. 



