196 CARNEGIE INSTITUTION OF WASHINGTON. 



for believing that some nebulse are composed of discrete solid mat- 

 ter, but it has not been shown that this has a quasi-gaseous organi- 

 zation. For the purposes of a critical discrimination it is necessary to 

 find grounds for supposing that this discrete solid matter is organ- 

 ized as a swarm characterized by heterogeneous movements involv- 

 ing collision and rebound in gaseous fashion, as distinguished from 

 revolutionary movements controlled by gravitation and inertia in 

 planetary fashion, which constitutes the planetesimal organization. 

 The two modes of organization are very distinct dynamically, though 

 they are likely to be more or less combined in any actual system. I 

 have given some time to a study of the possibilities of the origin of 

 such a quasi-gaseous assemblage of meteorites. The studies have 

 taken twolines^(i) the possibilities of assemblage from a primitive 

 diffuse condition, and (2) the possibilities arising from the dispersion 

 of some previous body. 



(i) Inspection of the problem made it clear that a grave difficulty 

 lies in the high ratio of the moving force to the gravitational force in 

 celestial bodies, on the average. The gravitational force is obviously 

 the chief agent to be assigned the work of bringing together and 

 holding together the meteoritic swarm in question, while the moving 

 force is the chief opposing or dispersing agent. The gravitative 

 power of individual meteorites over one another, at the distances 

 involved in the problem, is .exceedingly small, while the average 

 velocities of known meteorites is high and their moving force corre- 

 spondingly high. Estimated from present imperfect data, the aver- 

 age velocity of meteorites is of the order of 20 miles per second or 

 more. This is also about the average order of velocit}^ of stars, as 

 now determined, and hence it may fairly be assumed to be the order 

 of velocity of the average matter of the known universe, and may 

 be taken as the working basis for the problem in question. This 

 gives a prodigious kinetic energy to the matter to be assembled, 

 while the gravitative force between the small masses of dispersed 

 matter is relatively trivial. The individual attractions are all that 

 can be considered until after an assemblage is formed, and it is the 

 forynation of the assemblage that is here in question. 



So far as my studies have gone, almost the only conception that 

 seems to offer a remote possibility of the starting of a swarm of 

 meteorites under these adverse conditions lies in the exceptional 

 case of meteorites moving in nearly parallel directions at nearly the 

 same speed and in courses near one another. In this case the moving 

 forces of the meteorites have the same phase and only antagonize 



