704 Some Results of Gravitation. [December, 
The effect of gravity on the surface matter of the original 
nebula was almost wholly centripetal, the material of sur- 
rounding space being too rare to strongly attract it. If now 
we take the conceivable case that the original nebula was at 
one time of practically uniform density throughout, the 
centripetal gravity of the matter of this nebula would neces- 
sarily decrease regularly from surface to centre, there being 
a reverse attraction upwardly at every point below the sur- 
face. The first effects of compression would necessarily be 
superficial, and would at once modify this uniform decrease 
of gravity. The condensed matter would grow heavier in 
proportion to its density, its increased downward pressure 
overbalancing the upward attraction. Thus the first effect 
of compression would be to remove the region of greatest 
centripetal gravity to that point in the interior at which the 
increased weight produced by condensation was just balanced 
by the increased effectiveness of the centrifugal gravity. 
This point would descend more and more deeply as con- 
densation descended and grew more effective. But the dis- 
turbance of the original uniformity of gravity thus produced 
would be accompanied by a disturbance of an opposite cha- 
racter. As the gravity at any internal point must be deter- 
mined by the vigour of centripetal gravity diminished by the 
vigour of centrifugal gravity, it follows that, as the surface 
layer became condensed, the centrifugal gravity increased in 
vigour. Thus the layer of rare matter adjoining that of 
dense matter had its centripetal gravity, or its weight, de- 
creased. And this disturbance must have made itself felt, 
with diminishing effeCt, to the centre. If we take a portion 
of matter anywhere in the interior, this would experience 
two increments of attraction, — one from the matter laying 
between it and the nearest surface, the other from the matter 
in the line passing through the centre to the farthest surface. 
While all this matter was uniform in density, the vigour of 
these two lines of attraction would depend strictly upon their 
length. But when the matter at the two ends of the line — 
or the two surface regions — became condensed, these two 
portions of the line would exert increased attractions, in 
proportion to their density. But, under the law of diminu- 
tion of attraction with distance, this increased attraction of 
the near surface would considerably overbalance that of the 
distant surface. Therefore, with every increment of surface 
compression, the downward attraction of every portion of 
the rare interior matter must have decreased, this decrease 
making itself felt to the centre. 
Pursuing this thought we can readily conceive of a marked 
