i88i.] 
The Evolution of the Solar System. 
259 
there must be tradts of partial homogeneity, greatly varying 
in dimensions ; and also dense regions, probably contiguous 
to rare regions, marking out natural localities of minor 
aggregation. Thus there is reason to believe that, in the 
original mass, centres of force of greatly diversified influence 
displayed themselves, and that the minor aggregations re- 
sulting ranged in size from planetary to meteoric dimensions. 
It is probable, indeed, that this process affedted every portion 
of the mass, the condensing planetary masses being full of 
minor centres of aggregation of their own, and this possibly 
extending down to the formation of atomic masses from 
the heterogeneous aggregate. 
But we are here simply concerned with the original inde- 
pendent masses, not with their interior evolution. In respedt 
to the formation of these the centripetal attradtion of the 
whole mass must necessarily possess a vigorous influence. 
In regions near the centre this influence would be very pow- 
erful. The minor aggregations being there formed under 
the influence of a vigorous central attradtion must necessa- 
rily be smaller in size, as they could only affedt a limited 
region of the nebula. Their centripetal attradtion, at a cer- 
tain limited distance from their centres, would be over- 
balanced by the attradtion of the general centre, and all 
substance beyond this distance be swept off towards the 
solar centre. Of course the size of such minor aggregations 
must have depended upon the density of the matter from 
which they were originally composed, and they may thus 
have greatly varied in dimensions ; but they could not have 
assumed very great dimensions, on account of the over- 
mastering vigour of the central attradtion upon their out- 
lying regions. 
In the outer portions of the nebula the state of affairs 
would be markedly different. Here the vigour of central 
attradtion would be greatly reduced, and thus the influence 
of minor centres might extend to a much greater distance 
outwardly. Therefore vast regions of the nebula might be 
brought under the influence of a single minor centre, arising 
in a partly condensed portion of the mass, before the dis- 
tance from this centre became so great that its attradtion 
was overbalanced by that of the general centripetal force. 
Consequently, if the diffusion of the mass made any ap- 
proach to homogeneity, there must have arisen in it numerous 
minor masses, increasing in size outwardly with some regu- 
larity, and all subordinate in their general motions to the 
central attradtion of the whole mass. This centripetal 
attradtion must remain virtually the same whether the 
