554 Proceedings of Royal Society of Edinburgh. [sess. 
formed by the contraction of a rotating nebula. But the re- 
duction of rotary momentum in a system cannot be explained 
in absence of external forces ; and since such forces, acting with 
sufficient power, cannot be claimed, we must conclude that the 
formation of the planets must have been due to a cause different 
from that assumed by Laplace. In the following communication, 
which is of a merely suggestive character and is based on some 
conclusions arrived at in my previous paper on temporary stars, 
I have tried to avoid this difficulty by proposing a possible 
mode of development, in some respects different from Laplace’s 
view, but ultimately leading to the same conclusions. I assume 
that the conditions necessary for the formation of planets were 
introduced after the solar body had condensed from a won-rotating 
nebula into a spherical body of a diameter probably less than the 
distance of Mercury. I suppose that at this stage the solar body, 
on its course through space, had approached a cosmic cloud of 
meteoric constitution, and had passed through a series of events 
such as have been described in my previous paper, leading — as 
was shown there — to the formation of a ring of meteors rotating 
with orbital velocities round the solar nucleus. The question to 
be discussed is whether we may explain the formation of planets 
and their rotation round an axis simply from the heterogeneity of 
the ring and the mutual perturbing action of its constituents. 
The conclusion, although reached by somewhat general and ad- 
mittedly crude considerations, seems yet to be that these perturba- 
tions would introduce motions in the particles round a point of the 
ring where matter was denser than on the average, such as would 
impart a rotation to the. condensing planet in the required direction. 
There seems also reason to suppose that Professor Darwin’s in- 
genious conception of fluid-pressure in a meteoric swarm would 
sufficiently account for a gradual evacuation of the ring by the 
gravitational action of the planets. Lastly, I propose to show 
that the suggested view offers an explanation of the origin of 
comets compatible with observed facts, and may thus perhaps 
supplement the nebular hypothesis with regard to a point as to 
which Laplace’s theory gives no satisfactory account. 
In my paper, “ On Professor Seeliger’s Theory of Temporary 
Stars,” an attempt was formerly made to explain the genesis of 
