fundamental problems of geology. 255 



The Work of Dr. Moulton. 



Chicago, September 2g, igo^. 



Dear Professor Chamberlin : I regret that unforeseen con- 

 ditions have prevented me from working more than two months on 

 the nebular hypothesis in the last year. The prospects now are that 

 I shall be able to carr>' out the work of the exhaustive critical re- 

 view without further serious interruption. 



It has seemed to me essential to make a careful preliminary dis- 

 cussion before taking up the work professedly referring directly to 

 the nebular hypothesis. These preliminary discussions are on (a) 

 the different kinds of hj'potheses and their uses, {b) the observa- 

 tional data pertinent to the inquiry, and (f) the laws which have 

 been derived from the data. Then will follow the discussion of the 

 work done on the nebular hypothesis. The first epoch reaches up 

 to Laplace, the second consists of Laplace and the commentators on 

 his work, including the modifications introduced by the theory of 

 the conservation of energy ; the third starts with Darwin's work on 

 tidal evolution and reaches to our work in 1900. 



(a) Different Kinds of Hypotheses and Their Uses. — In this I have 

 attempted, in the first place, to analj^ze hypotheses with respect to 

 the character of their origin and relation to observational data. In 

 the second place, I have attempted to form an estimate of the value 

 of these various sorts of hypotheses in scientific work. I am firmly 

 convinced that this work is of value apart from the later discussions, 

 and that it is particularly valuable in connection with the estimates 

 of the work done on the nebular hypothesis by the various writers. 



(^) Observational Data. — This and the next topic are almost uni- 

 versally largely mixed. They are purposely sharply separated here, 

 for the observational data are a permanent acquisition, while the 

 laws are hypotheses derived from them. Since the final theory, the 

 nebular hypothesis, is in question, the preliminary hypotheses or laws 

 can not be passed over lightly. 



{_€) Scientific Laws. — This topic and the preceding have led me 

 into every field of physical science. The laws have been (and are 

 being) analyzed on the basis of {a) and their probable validity ex- 

 amined. This task of looking critically at the foundations of all 

 laws upon which the nebular hypothesis is based is very heavy. 



The preliminary discussions {a) and {b) are practically complete. 

 The work on (<r) has made some progress, but it largely remains to be 

 done. Most of the data on the nebular hypothesis have been col- 

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