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it is obvious that the larger granules of smaller surface curvature will lose less 

 and gain more, on the average, than the smaller granules of greater curvature. 

 It follows that the larger granules will grow at the expense of the smaller 

 [p. 194, "Contribution to the Theory of Glacial Motion," T. C. Chamberlin, 

 1904, the paper cited by the writer of the report]. 



In following the further discussions of the growth of snow granules, 

 the non-technical reader is quite sure to become bewildered by the 

 substitution of the concept of vapor pressure over the individual granules 

 for that of evaporation, in the author's citation and criticism of views 

 written years ago, especially in the absence of any explicit state- 

 ment of the sense in which the term "vapor pressure" is used; for 

 example : 



As regards the increase in mean size of the crystals, this, as has been pointed 

 out by Chamberlin,! should be carried out through the growth of the larger crystals 

 at the expense of the smaller ones, the action taking place for the reason that the average 

 vapour pressure over a small crystal is greater than that over a large crystal. [Italics the 

 reviewer's.] 



Several passages in Chamberlin's treatise are, however, obscure. Thus the 

 increased vapour pressure over a small crystal is said to be due to the increased curva- 

 ture of the surface, as is the case with water drops [pp. 1 18-19]. 



This is certainly taking extraordinary liberties in citation and in 

 making the mutilated citation the basis of criticism, for no mention 

 whatever is made of vapor pressure in the paper cited. A higher rate 

 of evaporation was assigned to sharper curvature. If the substitution 

 of vapor pressure for evaporation is intended to mean that vapor pressure 

 and evaporation are the same thing, it seems as though that should 

 have been so stated explicitly. Perhaps the reader would like a chance 

 to see for himself whether the obscurity grows out of the original point of 

 view or the substitute. 



The need for an explicit statement of precisely what is meant by vapor 

 pressure over the individual granules becomes the more obvious when the 

 ordinary use of vapor pressure comes into use as it does later in giving a 

 list of vapor pressures (p. 267). No hint that another sense of the 

 term "vapor pressure" is here given, but it is evident from the context 

 that the vapor pressures listed are the familiar partial pressures of the 

 water vapor of the atmosphere which are pressures upon the granules 

 actuated by the attraction of the mass of the earth. 



' T. C. Chamberlin, "A Contribution to the Theory of Glacial Motion," Decen- 

 nial Pubhcation. University of Chicago, Series I, 1904, Geology. 



