loo wherry: reply to dr. tutton's discussion 



as science advances; and this may be just as true in crystal- 

 lography as in any other field. In the paper under discussion^ 

 the writer endeavored to point out an instance where changes 

 in view-point appear to be needed, and is glad to take up Dr. 

 Tutton's criticism (preceding article) and to show that the 

 difference between us consists chiefly in our willingness to admit 

 the above proposition. Dr. Tutton's summary of the paper in 

 question is reasonably adequate; but whether that paper is 

 based on "misconceptions regarding fundamental facts" must 

 be decided by the reader of the present discussion. 



The magnificent research on diamond by Fersmann and 

 Goldschmidt- has surely established for all time the fact that 

 tetrahedral (Class 31) features are often shown by both the 

 habit and the etch figures of this mineral. The proof of the 

 absence of electric polarity by Van der Veen, which no attempt 

 has been made to discredit, can not alter that fact. What 

 is needed is an explanation of the apparent discrepancy, and that 

 is what the writer endeavored to supply. The structure of the 

 mineral having been established to the satisfaction of all con- 

 cerned by the Braggs, the writer saw therein a way to account 

 for the difficulty, for the structure as a whole, with which the 

 electric polarity is presumably connected, is admittedly holo- 

 hedral (Class 32) while the symmetry of the unit cells is tetra- 

 hedral (Class 31), which is reflected in the habit and etch-figures. 

 In other words, the writer accepts the correctness of the work 

 of all the authors, whereas those by whom diamond "has for 

 some time now . . . been considered as holohedral" must ignore 

 or discredit the work of Fersmann and Goldschmidt, as well 

 as overlook the significance of the Bragg demonstration that the 

 symmetry of the unit cell of diamond is less than that of the 

 structure as a whole. The last sentence of the writer's con- 

 clusion, which Dr. Tutton considers "absolutely, fundamentally 



' This Journal 8: 480. 1918. 



^ Through the writer's failure to correct proof of his paper the title of the work 

 by these authors was given as "Diament" instead of "Diamant." Also, the heading 

 of the last double column of the table should, of course, read "atomic." 



