1904-5.] Dr J. Halm on the Nebular Hypothesis. 
553 
Some Suggestions on the Nebular Hypothesis. 
By J. Halm, Ph.D. 
(MS. received March 6, 1905. Read March 20, 1905.) 
The hypothesis of Laplace on the genesis of the solar system 
from an extensive nebula presents difficulties of so serious a 
character that important modifications appear to be required in 
order to make it conformable with the laws of dynamics. The 
objection most frequently brought forward refers to the mode in 
which Laplace assumes the separation of the planets from the 
contracting nebula to have taken place. It is urged that the 
intermittent shedding-off of rings is a somewhat unintelligible 
process considering the physical,, constitution of the nebula ; that 
we should rather expect a continuous separation of particles at the 
equator, where the centripetal force is overbalanced by the centri- 
fugal force, and hence that no fissure of a large ring from the 
main bulk is to be expected. Much hope is now entertained that 
the brilliant researches of M. Poincare and Professor Darwin on the 
form of equilibrium of rotating fluids may eventually remove this 
difficulty, and teach us something about the evolution of the solar 
fluid when its axial rotation was quickening through contraction. 
It is conceivable that even in a heterogeneous body, as the solar 
nebula doubtless was, a course of events might take place which 
would lead from the sphere through the series of spheroids 
and Jacobi ellipsoids to Poincare’s well-known pear-shape ; and 
ultimately, by increasing constriction of the waist of the pear, to 
the division of the body into two or more. But even granting 
such a possibility, some difficulty is felt in approaching an 
explanation of solar evolution from this groove of thought, 
because, as Mr Moulton has pointed out, the solar nebula has not 
fulfilled the law of constant moment of momentum. There 
can be no doubt that the present sum of rotary moments is 
considerably less than it should be if the planets had been 
