60 Ms (En Glas d DIsILION 
The laws of dynamics afford a firm ground of inquiry so far 
as they can be brought into service. As applied to mass and 
momentum they are rigorous, and so far as they can be covered 
by satisfactory computation they are decisive. The purpose of 
the present paper is to set forth the results of an attempt to 
apply these laws to the nebular hypothesis in certain ways that 
are more or less unfamiliar. These results are the outcome of 
a joint inquiry by Dr. F. R. Moulton and myself. They are a 
part of the results of a more or less continuous study on related 
themes lying on the border-land of geology and astronomy, run- 
ning through the past three years. Our relations have been so 
intimate and our exchanges of ideas so free and so frequent that 
it is impossible to apportion the responsibility for the various 
-methods adopted and the modes of carrying them out. The 
higher mathematical work is, however, to be credited to Dr.. 
Moulton. It has perhaps been my function in the main to for- 
mulate problems and suggest general modes of attack, and Dr. 
Moulton’s to devise methods of analysis and bring to bear the 
mathematical principles of dynamics, but this has not been uni- 
formly so. Quite often we have proceeded by successive alter- 
nate steps in which each was the parent of its successor. In a 
paper in the Astrophysical Journal published essentially concur- 
rently with this, by mutual understanding, Dr. Moulton dis- 
cusses not only the bearings of the ratios of masses and momenta 
treated in this paper, but several other modes of testing the 
nebular hypothesis, some small part of which have been touched 
upon in my previous papers and some of which will be discussed 
in these pages later. The mathematical treatment of the present 
theme will be found in Dr. Moulton’s paper. 
For convenience and definiteness, the treatment here will be 
based on the Laplacian phase of the nebular hypothesis, but the 
conclusions will be found applicable, in all essential respects, to 
such meteoroidal modifications of the hypothesis as postulate a 
spheroidal form controlled by the laws of hydrodynamic equilib- 
rium. 
