418 THE INSTABILITY OF THE HOMOGENEOUS. 



set up in any direction becomes itself a cause of subsequent 

 motion in that direction, lie might further infer that the 

 heterogeneities thus set up would tend ever to become more 

 pronounced. Established mechanical principles would 

 justify him in the conclusion that the motions of these ir- 

 regular masses of slightly aggregated nebular matter to- 

 wards their common centre of gravity must be severally ren- 

 dered eurvelinear, by the resistance of the medium from 

 which they were precipitated; and that in consequence of 

 the irregularities of distribution already set up, such con- 

 flicting curvelinear motions must, by composition of forces, 

 end in a rotation of the incipient sidereal system. He might 

 without difficulty show that the resulting centrifugal force 

 must so far modify the process of general aggregation, as to 

 prevent anything like uniform distribution of the stars even- 

 tually formed — that there must arise a contrast such as we 

 see between the galactic circle and the rest of the heavens. 

 He might draw the further not unwarrantable inference, 

 that differences in the process of local concentration would 

 probably result from the unlikeness between the physical 

 conditions existing around the general axis of rotation and 

 those existing elsewhere. To which he might add, that 

 after the formation of distinct stars, the ever-increasing 

 irregularities of distribution due to continuance of the same 

 causes would produce that patchiness which distinguishes 

 the heavens in both its larger and smaller areas. "We 



need not here however commit ourselves to such far-reach- 

 ing speculations. For the purposes of the general argument 

 it is needful only to show, that any finite mass of diffused 

 matter, even though vast enough to form our whole sidereal 

 system, could not be in stable equilibrium; that in default 

 of absolute sphericity, absolute uniformity of composition, 

 and absolute symmetry of relation to all forces external to it, 

 its concentration must go on with an ever-increasing irregu- 

 larity ; and that thus the present aspect of the heavens is not, 

 so far as we can judge, incongruous with the hypothesis of a 



