THE STELLAR UNIVERSE. 



has ever been witnessed. The planetary nebulae, however, present 

 some very remarkable examples of these colours. Sir J. Herschel 

 indicates a beautiful instance of this, in a planetary nebula situate 

 in the southern constellation of the Cross. The apparent diameter 

 is 12", and the disc is nearly circular, with a well-defined outline, 

 and a " fine and full blue colour verging somewhat upon green." 

 Several other planetary nebula) are of a like colour, but more 

 faint. 



The magnitudes of these stupendous masses of stars may be 

 conjectured from their probable distances. One of the largest, 

 and therefore probably the nearest of them, is situate near the 

 star Ursse majoris (one of the pointers). Its apparent dia- 

 meter is 2' 40". Now, if this were only at the distance of 61 

 Cygni, whose parallax is known, it would have a diameter 

 equal to seven times that of the extreme limit of the solar 

 system; but as it is certain that its distance must be many 

 times greater, it may be conceived that its dimensions must be 

 enormous. 



In fig. 25 is represented a small nebula of this class, drawn by 

 Sir J. Herschel. It is situate near the star 5 in the constellation 

 Hercules (EA, 17 h 45 m NPD, 66 53'), and is described as having a 



Fig. 25. Fig. 26. 



perceptible disc from 1" to 1|" in diameter, surrounded by a faint 

 nebula. 



In fig. 26 is another similar object, situated a little to the north 

 of the constellation of Lyra (E A 19 h 40 m N P D 39 54'). A most 

 curious object. A star of the llth magnitude, surrounded by a 

 very bright and perfectly round planetary nebula of uniform 

 light. Diameter in EA 3 -5", perhaps a very little hazy at the 

 edges. (Herschel.) 



In fig. 27 is represented another of the same class, situated in 

 (R A 13 n 29 m B- P D 107 1') the constellation Yirgo near the bright 

 star Spica. Its entire diameter is 2', being the 15th of that of the 

 moon, and the diameter of the bright central part 10" to 15". It 

 is described as a faint large nebula losing itself quite impercep- 

 tibly ; a good type of its class. (Herschel.) 



In fig. 28 is a nebula, situate in (E A 10 h 28 m N P D 35 36'). It 

 28 



