NEBULAE. 



183 



by Herschel to our own sun, rejected at first by most philosophers, but now confirmed 

 by Argelander, is so far in favour of this view. In accounting also for that change of 

 temperature which the earth has undergone since vegetable productions appeared upon 

 its soil, the evidence of which we have in the remains of the ferns and palms of the 

 tropics in northern regions still existing. The continental investigators have not 

 overlooked the possibility of a gradual transition of the globe along with the solar 

 universe into colder regions of space. 



Besides resolved nebulae, or those whose constitution is unequivocally determined by 

 telescopic inspection, there is another class which range under the general head of resolv- 

 able, conceived to be actually identical with the former, that is, separate and vast schemes 

 of stars, which a sufficient increase of instrumental power would decisively prove. They 



are at present indefinite because of greater remote- 

 ness. The most singular object of this class is in 

 Vulpecula et Anser, on the breast of the Fox, No. 27. 

 in Messier's catalogue, first discovered in the year 

 1 764. The whole figure is that of an oblate spheroid ; 

 but it is easy to trace the shape of a dumb-bell or hour- 

 glass composed by the two connected dense hemi- 

 spheres. No form parallel to this has yet been found 

 in the heavens. Since the great reflector at Birr 

 Castle has been completed, it has been turned upon 

 this nebula by the Earl of Rosse, and some hope of 

 resolving it has been announced. The diameter 

 -beii Nebula. drawn through the centres of the two hemispheres 



amount to 5', which gives an immense extent to the whole. But the most interesting 

 object of the class under notice is a halo nebula, discovered by Messier in 1772 in Canes 



Venatici. It is near the back of the northern hound 

 Asterion, about 5 south by west of Benetnasch, 

 the last star in the tail of the Great Bear. This has 

 been called a ghost of the planet Saturn as seen with 

 his rings in a vertical position. It exhibits a bright 

 central nucleus, surrounded with a distant luminous 

 annulus split through part of its circumference, a fac- 

 simile of our sidereal firmament with its divided 

 Milky Way, as espied from a similar distance in the 

 same direction. It is number 1623 of Sir John 

 Herschel's catalogue ; and " supposing it," he re- 

 marks, " to consist of stars, the appearance it would 

 present to a spectator placed on a planet attendant 

 on one of them, eccentrically situated towards the n. p. quarter of the central mass, 

 would be exactly similar to that of our Milky Way, traversing, in a manner precisely 

 analogous, the firmament of large stars into which the central cluster would be seen 

 projected, and (owing to its greater distance) appearing, like it, to consist of stars 

 much smaller than those in other parts of the heavens. Can it then be that we have here 

 another system, bearing a real physical resemblance and strong analogy of structure to 

 our own?" There are various other forms of resolvable nebulas. Miss Herschel, with 

 a small Newtonian telescope, in August, 1783, discovered one of a lenticular shape, of 

 which Sir John Herschel has given a drawing. Its real form is supposed to be that of 

 an immense ring resembling our Milky Way, appearing elongated, owing to its lying in 

 a direction oblique to our line of vision. This object is in Andromeda, nearly upon a 



Halo JNeoula. 



