674 T. C. CHAM BERLIN 



took the form of concretions or of crystals. I have ventured to 

 suggest that this may be the mode in which chondrules — Httle 

 Organized bodies that enter into the formation of 90 per cent of 

 known meteorites — ^were formed. Later I shall suggest that the 

 formation of the common small meteors of the sky may have 

 taken place in practically the same way as planetesimals, i.e., by 

 the progressive aggregation of precipitates from the stony and 

 metallic ingredients of solar gases shot into interplanetary space 

 and there cooled, the distinction between the two being their 

 orbital characters and planetary relations. If these suggestions 

 are in the line of truth, the chondrules give very specific evidence 

 on the usual sizes of planetesimals, for they range from the size 

 of a walnut down to fine dustlike particles. 



4. The negative evidence. — Concurrent with these concrete 

 sources of evidence, supported by theory, is the significant fact 

 that no bodies of a distinctly larger or planetoidal order of magni- 

 tude are seen to revolve in the region of the earth's orbit or within 

 it. We have found reasons for suspecting that the normal dynamic 

 stresses in this inner solar region have always been too great to 

 permit the collective aggregation of precipitate clouds of so little 

 mass. At any rate, the negative testimony of observation stands 

 against any view that postulates an abundance of bodies of plan- 

 etoidal size in the region of the earth or their effective participation 

 in the formative processes of the earth or the moon. 



Let us then assume that the chondrules are our best natural- 

 istic guide in respect to the normal sizes of planetesimals. For 

 definiteness in the computations that follow, let us assume as a 

 convenient representative weight, one-fiftieth of a pound, say one- 

 third of an ounce, or about 9 grams. In testing the probability, 

 or otherwise, that planetesimal infalls would produce a molten state 

 of the growing earth-core, it will make no essential difference 

 whether the planetesimals were somewhat larger or somewhat 

 smaller than this size which is adopted merely for definiteness 

 and convenience. After inspection of the melting effects in a case 

 thus made as nearly normal as we conveniently can, we will try to 

 test the effects of supposedly larger planetesimals. 



