10 EXPLANATIONS. 



that there is only one class of nebulee, that the 

 hypothesis will suffer. Such, at least, I conclude 

 to be the sense of a passage which I take leave to 

 transfer, in an abridged form, from a recent edition 

 of Professor Nichol's work. 



" I. By far the greater number of the milky streaks, or 

 spots, whose places have hitherto been recorded, lie at the 

 outermost, or nearly at the outermost boundary of the sphere 

 previously reached by our telescopes : and in this case there 

 is no certain principle on the ground upon which a pure 

 nebula can be distinguished from a cluster so remote that 

 only the general or fused light of its myriads of constituent 

 orbs can be seen. Sometimes, — resting on a peculiarity of 

 form or other characteristic, — the astronomer may venture a 

 guess that such an object is probably a firmament ; as, indeed, 

 I was bold enough to do in former editions of this work with 

 regard to several which have since been resolved ; but, in the 

 main, he can tell little concerning them, or have any other 

 belief, than that, as with similar masses near him, a great, 

 probably the greater number, are true clusters, grand arrange- 

 ments of stars, incredibly remote, but resembling m all things 

 our own home galaxy. Now, the application to such objects 

 of a new and enlarged power of vision, could be attended only 

 by one result — magnificent, but far from unexpected : and it 

 is here that the six-feet mirror has achieved its earliest 

 triumphs. Under its piercing glance, great numbers of the 

 milky specks have unfulded their starry constituents ; some 

 of these, which previously were almost unresolved, shining 

 with a lustre equivalent to that of our brightest orbs to the 

 naked eye. How far it will go with its resolving power has 



