I40 T. C. CHAMBERLIN 



but the relative rates of revolution that brought this about would 

 destroy it. Collectively, the planetesimals would be so distributed 

 that they would have almost no concentrating force of their own 

 that was not later reversed or neutralized by their own orbital 

 motions. 



2. Practically the whole aggregation, then, would be that of 

 the formation of discrete particles such as started with the joining 

 of molecules and were built up thence into crystals, pellets, nodules, 

 or whatever these might grow into later. The chemical combina- 

 tion of molecules would take place at proper temperatures readily 

 enough by simple contact, whether this arose from collision while 

 in the state of a gas, or from contacts brought about by planetesimal 

 motion, or otherwise. Such refractory chemical compounds as 

 now form the main mass of the solid bodies of the moon, Mars, 

 Venus, and the earth, would probably be formed at high tempera- 

 tures while they were still a part of the postulated nebula. The 

 critical feature of the case Hes in the way these complex refractory 

 molecules would be gathered together after they were formed. 

 While they remained in a free state as molecules they would 

 normally tend to rebound on collision as molecules do and so 

 maintain their free state. Even if they were brought together 

 under conditions favorable to remaining together, their rotations 

 or vibrations would tend to throw them apart, as would also sub- 

 sequent colhsions. To overcome these adverse influences, there 

 was need for some special uniting agency, as is well recognized in 

 the familiar case of the formation of the globules of fogs and 

 clouds from water vapor in the atmosphere. It was long supposed 

 that there must be a dust particle or some similar aggregate to 

 serve as a collecting center (the "seed," X, above) ; but it was later 

 found that molecules electrically charged serve this function also. 

 In our problem, the formation of the first minute aggregates is the 

 very crux of the question, and we cannot assume the existence of 

 any such dustlike aggregates as the means of starting the process. 

 But molecules electrically charged would probably be freely 

 developed by friction, by the action of ultra-violet light, and by 

 other means, and such charged molecules might well serve as the 

 "seed" for starting the minute aggregates. 



