(jgO PHILOSOPHICAL TRANSACTIONS. [ANNO 1785. 



have drawn together the rest. Now, to have some idea of the wonderful extent 

 of this system, it may he observed that this section of it is drawn on a scale 

 where the distance of Sirius is no more than the 1 50th part of an inch ; so that 

 probably all the stars, which in the finest nights we are able to distinguish with 

 the naked eye, may be comprehended within a sphere, drawn round the large 

 star near the middle, representing our situation in the nebula, of less than the 

 15th part of an inch radius. 



The Origin of nebulous Strata. — If it were possible to distinguish between the 

 parts of an indefinitely extended whole, the nebula we inhabit might be said to be 

 one that has fewer marks of profound antiquity on it than the rest. To explain 

 this idea perhaps more clearly, we should recollect that the condensation of 

 clusters of stars has been ascribed to a gradual approach ; and whoever reflects on 

 the numbers of ages that must have passed before some of the clusters, that will 

 be found in my intended catalogue of them, could be so far condensed as we find 

 them at present, will not wonder if I ascribe a certain air of youth and vigour to 

 many very regularly scattered regions of our sidereal stratum. There are also 

 many places in it where there is the greatest reason to believe that the stars, if 

 we may judge from appearances, are now drawing towards various secondary 

 centers, and will in time separate into different clusters, so as to occasion many 

 subdivisions. Hence we may surmise that when a nebulous stratum consists 

 chiefly of nebulae of the 1st and 2d form, it probably owes its origin to what may 

 be called the decay of a great compound nebula of the 3d form ; and that the sub- 

 divisions, which happened to it in length of time, occasioned all the small nebulae 

 which sprung from it to lie in a certain range, according as they were detached 

 from the primary one. In like manner our system, after numbers of ages, may 

 very possibly become divided so as to give rise to a stratum of 2 or 300 nebulae ; 

 for it would not be difficult to point out so many beginning or gathering clusters 

 in it. This view of the present subject throws a considerable light on the appear- 

 ance of that remarkable collection of many hundreds of nebulae which are to be 

 seen in what I have called the nebulous stratum of Coma Berenices. It appears 

 from the extended and branching figure of our nebula, that there is room for the 

 decomposed small nebulae of a large, reduced, former great one to approach nearer 

 to us in the sides than in other parts. Nay possibly there might originally be 

 another very large joining branch, which in time became separated by the con- 

 densation of the stars ; and this may be the reason of the little remaining breadth 

 of our system in that very place : for the nebulae of the stratum of the Coma are 

 brightest and most crouded just opposite our situation, or in the pole of our 

 system. As soon as this idea was suggested, I tried also the opposite pole, where 

 accordingly I have met with a great number of nebulae, though under a much 

 more scattered form. 



