D. Trowbridge on the Nebular Hypothesis. 349 
- ? 
at a motion of rotation would result from the cooling down 
of the nebulous mass, the attraction of gravitation, and other 
forces of nature which might operate. 
12. The preceding general considerations may be regarded as 
applying with more force to the development of the sidereal sys- 
tems, such as the Milky Way, and other starry clusters, than to 
the formation of the solar system, or to any single system of a 
sun and the planets which revolve around it. We have now 
given a sufficiently lucid exposition of the development of the 
Starry systems—the island universes—for our present purpose.” 
We shall now descend from these general considerations in ref: 
erence to the structure of the universe, to a view of the princi- 
ples which governed the formation of the solar system, accord- 
ing to the nebular hypothesis, and thus to see how far we are 
able to go in accounting for the general structure of that system 
i of which we more immediately form a part. It is mainly in this 
part of our subject that we must look for that proof of the truth 
: of the nebular hypothesis which will be in any great degree 
Satisfactory. 
ditions are almost impossible,—perhaps quite so in nature,—we 
see th 
original nebulous mass broke up before they took that form— 
hecessarily symmetrical—which the conditions of equilibrium 
require, we have evidence that the smaller division, the single 
nucleus from which the solar system was developed, had so far 
that form may have been. : : 
14. A fluid mass which does not rotate on an axis must ulti- 
mately become spherical in form, whatever be the law of attrac- 
fon." But if it have a rotatory motion, it can never become a 
s: a more complete discussion of that part of our subject which pies to the 
formation of the starry clusters, see a very able treatise by Stephen A a 
LL.D., Professor of Natural Philosophy and Astronomy 1n the College of New Je 
wa published in Gonld’s Astronomical Journal, vol. ii, and entitled, On ” gin 
the Forms and the Present Condition of some of the Clusters of Stars and several 
of the Nebule. It occupies 29 pages 4to. 
_ ~~ Courtenay’s Mechanics, p. 355. 
