D. Trowbridge on the Nebular Hypothesis. 25 
Art. IV.—On the Nebular Hypothesis; by DAviD 
TROWBRIDGE, A.M. 
[Concluded from vol. xxxviii, p. 360.] 
1. The Breaking-up of the Rings. 
34. The process of cooling would still continue after the rings 
had separated. The loss of caloric from radiation would cause 
the rings to contract their dimensions; and this, the unequal 
density of different parts, and the extraordinary perturbations to 
which they would necessarily be subject in their motions, would 
cause a separation of the rings in certain weak places. When 
once broken into parts while the density of the ring was very 
small, even if the parts were not many, the case would be extra- 
ordinary in which the parts would be prevented from re-uniting 
into a single planet, owing to the very great perturbations to 
which their motions would be subject, as separate bodies. It is 
impossible at present to tell just how a ring would be resolved 
into a planet. A system of waves would probably be developed, 
owing to perturbations; and by an accumulation in one part, 
owing to the nature of the disturbing force, such as calculation 
. may now ask in what direction the planet thus 
formed would rotate? The direction of rotation would depend 
on circumstances. Let us take the breadth of the ring from 
which Uranus was formed, the same as the diameter of his 
Aide of attraction in Kirkwood’s Analogy. The diameter of 
he sphere of attraction of Uranus, as given by Professor Kirk- 
wood,” is 7-438, The inner radius is 2558, and the outer one, 
4879. If we suppose the inner and the outer parts of the 
ring each to have the velocity due it according to Kepler's third 
law, then, the velocity of the inner part being called 1, that of 
, of the rings, but one or another will be approximated to, accor 
® This Journal, [2], xiv, }. 213. : 
Am. Jour. Sc1.—Szconp Sentes, Vou. XXXIX, No. 115.—Jay., 1865. 
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