Views on Prenehular Conditions. — A. Winchell. 201 
tion is essentially a gross fluid, and might manifest the behav- 
ior of a fluid. 
Professor G. H. Darwin undertook the analytical investiga- 
tion of this question, '"and in a memoir of extraordinary inter- 
est, established the following conclusions :— As far as frequency 
of collision is concerned, the hydrodynamical treatment .of a 
swarm of meteorites is justifiable; the aggregation may be 
treated as possessing a coefficient of viscosity such that if ro- 
tating, it would revolve nearly without relative motion of its 
parts, other than the motion of-agitation; but in later stages 
the viscosity would be diminished to such extent that the 
central portion would probably rotate more rapidly than the 
outside — as some phenomena suggest to have been the case in 
our system. A further conclusion is, that the larger and less 
frequently colliding meteorites will gradually settle toward the 
centre, leaving the smallest and most frequently colliding me- 
teorites — or fragments, particles or molecules — disposed at 
and near the surface, thus creating a maximum density about 
the centre, though its distribution is not according to the law 
of an elastic gas. It is further suggested that in the late 
stages of evolution, the meteors would be mostly absorbed by 
the central sun and planets, that their relative motion of agi- 
tation would be largely diminished, and that they would pro- 
bably move in clouds — "the dust and refuse of the system" — 
with so infrequent inter-collisions that it might not be permis- 
sible to treat the cloud as possessing the mechanical proper- 
ties of a gas. 
A very different conception of the prenehular history of 
matter was suggested by Dr. James Croll, twenty-one years 
ago." This supposes "that our sun was formed from a hot 
gaseous nebula produced by the colliding of two dark stellar 
masses, and that as the stars are suns like our own, they in 
all likelihood, had a similar origin." The considerations 
'* His results are embodied in a memoir "On the mechanical Condi- 
tion of a Swarm of Meteorites, and on Cosmogony," read Nov. 15, 
1888, before th^ Royal Society, and published in i\iQ Transactions , vol. 
180, A. pp. 1-69, with notes by the author to Dec. 19, 1888. The writ- 
er is indebted to professor Darwin for a copy. 
^''Philosophical Magazine .May, 1868. The thoutrht has been several 
times reproduced. "Climate and Time" chap. 21 ; (juarterhj Joxir. Set. 
July. 1877; Phil, Mag., July, 1878; "Climate and Cosmology," chaps. 
XVII, XVIII and xix ; "Stellar Evolution," 1889, 12mo, 218 pp". For the 
last two works named the writer acknowledges his obligations to their 
author. 
