200 Views on Prenebular Conditions. — A. Winchell. 
comet is coursing round the sun as a whole, the individual 
members will themselves gravitate toward each other. * * * 
The stones colliding will generate heat, and some gas will be 
evolved ; some members of the mass will be quickened, while 
other constituents of the mass will be retarded in their motion. 
* * * The result of these collisions would be such a 
smashing up of the constituents of the swarm that much fine- 
ly attenuated material would be left behind, sufficient to re- 
flect sunlight and to give rise to phenomena of the tail".'^ 
Thus the suggestion came into existence that some of the 
nebulse, as well as comets, are simply aggregations of stones, 
sand, fire mist and gases. This at least, was specifically enun- 
ciated by the present writer. Professor Lockyer inclined to 
adopt such a view of the constitution of nebulae, as is shown 
in the ample and interesting series of papers referred to. In 
one of these he says : "The brighter lines in the spiral nebulae, 
and in those in which a rotation has been set up, are in all 
probability, due to streams of meteorites with irregular mo- 
tions out of the main streams, in which the collisions would 
be almost ;i?7. It has already been suggested by professor G. 
Darwin \^N'ature volume xxxi, 1884-5, p.25] — using the gaseous 
hypothesis — that in such nebula) "the great mass of the gas is 
non-luminous, the luminosity being an evidence of condensation 
along lines of low velocity, according to a well known hydro- 
dynamical law. From this point of view, the visible nebula 
may be regarded as a luminous diagram of its own stream- 
lines.'"-^ 
The question naturally arose whether a svt'arm of discrete me- 
teoric bodies, in an aggregation of nebular dimensions, would 
manifest the behavior of a cooling and shrinking spheroid of 
gas. The essential conception of the nebular theory of the Solar 
system involves an elastic fluid and the conservation of an equi- 
librium figure, while -the meteoroidal aggregation presents at 
first view, a discrete condition of solid constituents quite lacking 
the distinguishiaig properties of a fluid. As soon, however, as 
we conceive the constituents in a perpetual state of collision 
and rebound, the physical movements of fluid molecules are 
at once suggested, and we perceive that within certain limits 
of distance of the meteoric constituents, the meteoric aggrega- 
1* Nature, xxxix, 402. Feb. 2] , 1889. 
'^Nature, Nov. 17, \S%1 ; Roy Soc . , Nov. 15, 1887. 
