218 GEOPHYSICAL THEORY UNDER THE PLANETESIMAL HYPOTHESIS. 



These results do not exclude the occurrence of more than two zones, 

 alternating with fall and rise of temperature, but inspection of the anal- 

 ogous expansions for intermediate points seems to indicate that this would 

 demand variations of p, o, X which differ widely in character from those 

 thus far postulated, and which are perhaps improbable, but whose proba- 

 bility it is difficult to estimate with the meager data at hand. 



Comparison of the various cases carried out in the computations gives 

 a fairly definite idea of a thermal process which, from the general point 

 of view hitherto adopted, can be considered characteristic of the planetes- 

 imal hypothesis so far as concerns independence of particular hypotheses 

 respecting the density, conductivity, and specific heat. Under the basic 

 assumptions made, the balance of evidence seems to favor its substantial 

 correctness in qualitative features, and even in general order of numerical 

 magnitudes, since the chief allowances to be made in the latter can be esti- 

 mated with confidence from the theory itself. For example, the lengths of 

 time involved may be overrated, about in the ratio that the true conduc- 

 tivity in the interior surpasses, as it probably does, the value used, which 

 is that obtained by observations on the rather loosely aggregated material 

 accessible at the surface. 



There seems to be sufficient reason for supposing the energy of impact 

 to have little influence in determining the primitive temperature, espe- 

 cially if the impinging particles be retarded seriously by an atmosphere. 

 But aside from this there have been made certain general assumptions, 

 which, though fundamental in the foregoing theory, seem to be arbitrary 

 rather than essential to the general hypothesis, and thus to demand criti- 

 cal examination. This will be attempted in Part III, in connection with 

 the development of an alternative theory intended to aid in estimating the 

 allowance which should be made for possible modifications of some of these. 



