IS Biog^raphkal Memoir of' Sir William HcrsclicL 



reason emanates, has given him the power of forming, as it were, 

 new organs for himself. From time immemorial, sensible 

 changes have been observed in the colour and brightness of se- 

 veral stars ; new stars have been seen all of a sudden bursting 

 forth into brilliancy, and, like ignited bodies, gradually fading 

 and disappearing, having, perhaps, been converted into unillumi- 

 nated orbs, and for ever withdrawn from our view. The proper 

 and always extremely slow motions of a pretty large number of 

 stars have been observed, or the alternating and periodical va- 

 riations of some of these bodies. A more perfect knowledge of 

 the history of the heavens is without doubt reserved for the ge- 

 nerations to come. We can only, at present, hope for fixed and 

 accurate results, like those of planetary astronomy ; we are con- 

 fined to the description of the present state, and the distinction 

 of the general characters of phenomena. The invention of te- 

 lescopes, and especially HerschePs observations, have ^iven a 

 prodigious extension to this branch of celestiaWphysics. 



We shall not here enumerate all the cosmological views of 

 this great astronomer. The exposition of so extensive a theory 

 would exceed the limits assigned to us ; but we shall point out 

 some of its principal features. He ranks in the first class the 

 stars which he names isolated, that is, such as are separated 

 from the others by immense intervals, and do not appear sub- 

 ject to a mutual action, whose effect is appreciable. He then 

 considers the double or triple stars, or the more complex side- 

 ral assemblages, whicli are systems of luminous bodies, evident- 

 ly approximated and retained by an existing cause, and move 

 together round a common axis. 



He next passes to the description of the nebulosities, or those 

 milky-looking and confused spots irregularly scattered through- 

 out the heavens. He chiefly observed the Milky Way, which he 

 considered as a single nebulosity formed of many millions of 

 stars. In it he saw more than fifty thousand traverse the field 

 of his telescope in an hour. All these stars are distributed in a 

 multitude of layers of great extent, in longth and breadth, and 

 so superimposed, that the thickness of the system is much 

 smaller than the other two dimensions. The stars which appear 

 to us to be the brightest belong to the Milky Way. This is also 

 the case with the sun, the centre of our planetary orbits, and it 



