PORTION OF THE COSMOS. NEBULAE. 235 



Toulouse in 1779,, when the comet discovered by Bode 

 came into its vicinity. Its apparent magnitude is nearly 

 equal to that of Jupiter's disk, and it is elliptical, the 

 proportion of its diameters being as 4 to 5. The interior 

 of the ring is by no means black, but rather somewhat 

 illuminated. Sir William Herschel had recognised some 

 stars in the ring, and Lord Hosse and Mr. Bond have now 

 entirely resolved it ( 404 ). On the other hand, the fine annular 

 nebulae of the southern hemisphere, Nos. 3680 and 3686, 

 are perfectly black in the interior of the ring. No. 3686, 

 moreover, is not elliptical but perfectly round ( 405 ) ; all 

 are probably annular or ring-shaped clusters of stars. It is 

 to be remarked that with the increase of optical means, both 

 elliptical and annular nebulae appear generally less defined in 

 their outlines : in Lord Rosse's telescope the ring-nebula in 

 Lyra even appears as a simple ellipse, having singular diverg- 

 ing thread-like nebulous appendages. It is especially striking 

 to observe the transformation of the nebula which, seen 

 through feebler telescopes, appears simply elliptical, into 

 Lord Eosse's Crab-Nebula. 



A class of phenomena less rare than annular nebulae, but 

 of which Sir John Herschel counts only 25, almost three- 

 fourths being in the southern hemisphere, consists of what 

 are called planetary nebulae, which were first discovered 

 by William Herschel, and are among the most wonderful 

 of celestial phaenomena. They have a most striking resem- 

 blance to the disks of planets. In the greater number of 

 instances they are either round or somewhat oval ; some- 

 times with sharply defined boundaries, and sometimes with 

 confused and vaporous edges. The disks of several have a 

 very uniform light ; others are " mottled or of a peculiar 



