138 T. C. CHAMBERLIN 



disruptive belt just outside the rim of the rotating spheroid (IV 

 above) must have had a notable development. If it were quite 

 safe to assign it the full breadth of the Roche limit, which holds so 

 well in the case of Saturn's rings, it would have had, taking the 

 earth stage as a mean, an outward reach of 133,000,000 miles. 

 But let us follow the safer course of using the conservative criterion 

 of Moulton which gives a zone of 35,000,000 miles (IV above). 

 Let it be recalled that the fragments of a disrupted mass revolving 

 about the controlling body under the conditions of this case take 

 orbital courses more or less parallel with one another. If the 

 gaseous rim of the nebula could have been "thrown off" as a 

 coherent body, it would not only have been disrupted into minute 

 constituents, but these would have been given orbits of a type 

 much hke those pursued by the particles in Saturn's rings, all the 

 more because the constituents of a gas tend to disperse themselves 

 by their own interaction. This is equivalent to saying that the 

 dynamic conditions within this zone were such as to inhibit any 

 aggregation of this material into a common large body like the 

 earth. Mars, or Venus, or into a lesser number of bodies of any 

 considerable size. Even when such scattered orbital matter was 

 left by the withdrawal of the nebula in the less intense horizons of 

 the nebular field of force, its aggregation would still be greatly 

 embarrassed by the superior control of the central mass. It is a 

 common error to think of such scattered matter as though it were 

 in neutral space entirely free from all forces except its own mutual 

 attractions. The control of the central body so far embarrasses 

 the assemblage of minute particles under the actual conditions of 

 such a case as this as to render their aggregation into a single 

 body improbable, as Moulton has so effectually shown.' 



However, for the sake of seeing its bearings on the problem in 

 hand, let us waive this improbabihty and try to follow the aggre- 

 gation of^the minute constituents of a quasi-Saturnian ring "thrown 

 off" from the postulated rotating nebula.^ 



I F. R. Moulton, ''An Attempt to Test the Nebular Hypothesis by an Appeal to 

 the Laws of Dynamics," Astrophys. Jour., XI (1900), p. 115. 



^ The deduction that the molecules shed by centrifugal action from a rotating 

 gaseous spheroid would pass into individual orbits and form a planetesimal system 

 does not depend solely on the Roche effect, as shown in "The Bearing of Molecular 

 Activity on the Spontaneous Fission of Gaseous Spheroids," Publication No. 107, 

 Carnegie Institution of Washington, 1909, pp. 161-67. 



