62 Ms (Op (CLEAN EMPIRIC ION, 
The distribution of density in the sun is unknown. If it 
follows Laplace’s law the rotatory momentum is .444. If it be 
regarded as homogeneous, the rotatory momentum is .679. This 
latter is certainly too large, and the former number is probably 
much nearer the truth, but the larger number is used in the 
greater part of the computations because it 1s more favorable to 
the Laplacian hypothesis. 
To obtain the rotatory momentum of the ancestral nebula it is 
necessary to consider its form, extent, and the variation of its 
internal density. By hypothesis the form was an oblate sphe- 
roid, but the exact degree of polar flattening is unassigned. 
Simple inspection, as well as mathematical analysis, shows that 
a given mass of matter rotating as a sphere will have a less 
-moment of momentum than when it takes the form of an oblate 
spheroid, the time of rotation and other factors being equal. If 
a yielding sphere be rotated it takes the spheroidal shape because 
that is the form of equilibrium for the added rotational momen- 
tum), and is) an expression: of such, additions Silom onesie 
Laplacian hypothesis the benefit of every doubt, the moment of 
momentum of the nebula is computed on the basis of a sphere. 
So also to favor the hypothesis, the nebula is made to reach 
merely ¢o the orbit of the derived planet, not to extend beyond 
it as is usually and necessarily assumed. In computing the rota- 
tory momentum of the whole nebular mass just before Neptune 
was separated, it is assumed that it reached only to Neptune’s 
orbit, whereas the nebular border must prey have extended 
some 500 million miles beyond. 
As this question of the distribution of the matter from which 
the planets were formed under the Laplacian hypothesis has 
other applications, it may be remarked here that in the forma- 
tion of a planet from a ring of dispersed matter the planet must 
assume such a point within the ring as to preserve the moment 
of momentum of the mass. In asymmetrical ring this point is 
somewhere near the center of the cross section. Though sub- 
ject to some qualifications from the greater circumference of 
the outer part and the possibly greater density of the inner part 
