376 NEBULAE. SECT, xxxvu. 



that they are not to be reckoned by hundreds : on a 

 rough computation, it appears that many clusters of this 

 description must contain ten or twenty thousand stars 

 compacted and wedged together in a round space, 

 whose area is not more than a tentiypart of that covered 

 by the moon ; so that its center, where the stars are 

 seen projected on each other, is one blaze of light 

 (N. 225). If each of these stars be a sun, and if they 

 be separated by intervals equal to that which separates 

 our sun from the nearest fixed star, the distance which 

 renders the whole cluster barely visible to the naked eye 

 must be so great, that the existence of this splendid as- 

 semblage can only be known to us by light which must 

 have left it at least a thousand years ago. Occasionally 

 clusters are so irregular and so undefined in their outline 

 as merely to suggest the idea of a richer part of the 

 heavens. These contain fewer stars than the globular 

 clusters, and sometimes a red star forms a conspicuous 

 object among them. Sir William Herschel regarded 

 them as the rudiments of globular clusters in a less ad- 

 vanced state of condensation, but tending to that form 

 by their mutual attraction. 



Multitudes of nebulous spots are to be seen on the 

 clear vault of heaven, which have every appearance of 

 being clusters like those described, but are too distant to 

 be resolved into stars by the most excellent telescopes. 

 Vast numbers also appear to be matter in the highest 

 possible degree of rarefaction, giving no indication what- 

 ever of a stellar nature. These are in every state of 

 condensation, from a vague film hardly to be discerned 

 with telescopes of the highest powers, to such as seem 

 to have actually arrived at a solid nucleus. This nebu- 

 lous matter exists in vast abundance in space. No 

 fewer than 2000 nebulae and clusters of stars were ob- 

 served by Sir William Herschel, whose places have 

 been computed from his observations, reduced to a com- 

 mon epoch, and arranged into a catalogue in order of 

 right ascension by his sister, Miss Caroline Herschel, a 

 lady eminent for astronomical knowledge and discovery. 

 Six or seven hundred nebulae have already been ascer- 

 tained in the southern hemisphere ; of these the Ma- 

 gellanic clouds are the most remarkable. The nature 



