i88i.] 
Some Results of Gravitation, 
707 
In such a manner the earth may have reached, or may 
eventually reach, its final state of condensation, this in- 
creasing downward to a certain distance from the surface, 
and thence decreasing to the centre, and being at every 
point in accordance with the effective gravitation, the 
pressure, and the physical state of its material at that 
point. 
The above considerations lead to some thoughts on the 
constitution of atoms. It is certainly not unreasonable to 
conclude that in the formation of atoms the same laws of 
fluid aggregation are obeyed as display themselves in the 
formation of suns and planets. There can be no question 
of great and small in the operation of natural laws, though 
differences in physical condition between great and small 
might produce certain differences in results. Thus the 
effects produced by solidification in great masses would not 
display themselves in minute masses. So the heterogeneity 
of great nebulous masses might be replaced by homogeneity 
in minute masses. These differences might produce differ- 
ences in results, but under like conditions the law of aggre- 
gation must act uniformly, without distinction of great or 
small. 
In a completely homogeneous nebulous mass condensation 
must proceed uniformly ; there could be no minor centres of 
aggregation, and no rotation of the mass, since every tend- 
ency to produce rotation in any one direction must be 
counteracted by an equal opposite tendency. In a hetero- 
geneous mass minor centres of aggregation must display 
themselves, and the tendency to rotate in certain directions 
must overbalance that in others. It may be well to remark 
here, also, that all these processes would proceed simulta- 
neously, so that the formation of the various bodies of the 
Solar System — as considered in my paper in this Journal 
for May, 1881 — must have been simultaneous, instead of 
successive, as commonly considered. 
The secondary centres of gravity in the original solar 
nebula affected gas volumes of the greatest diversity in size, 
from the planet down to the atom. The subordination of 
each such aggregate to the greater aggregate of which it 
formed part was an external, not an internal one, and it is 
very probable that the same principles of aggregation affected 
alike the sun and the atom. 
We may imagine several modes of atom formation. In 
the case of its arising through the centripetal attraction of 
a mass of matter, this matter might be homogeneous and 
might be heterogeneous in density. In the former case all 
