386 SCIENCE PROGRESS 



viscous flow observed in the latter, the walls of the cavity 

 disintegrate with the projection of minute particles, the disin- 

 tegration increasing as the pressure rises. Neither the mode 

 of disintegration nor the arrangement of cracks which some- 

 times developed bore any apparent relation to the crystalline 

 structure. Even when subjected to a pressure of 30,000 kg/cm 2 , 

 finely powdered quartz, felspar, or talc could not be welded 

 together, and this is explained as due to the existence of thin 

 films of air between adjacent grains, preventing sufficiently 

 close contact. In a second paper (ibid. pp. 269-80) the stress- 

 strain relations in crystalline cylinders is treated mathemati- 

 cally. Although a rigorous solution cannot be obtained, it 

 is possible to get a first-order approximation for cubic and 

 tetragonal crystals and a second-order approximation for 

 trigonal crystals. 



E. T. Wherry (Jour. Washington Acad. Sci. 8, 277, 319, 

 191 8) has attempted to find a relation between the refractive 

 indices and the axial ratio in the case of tetragonal crystals. 

 It is found that the ratio of the " refractions," as obtained 

 from the Lorentz-Lorenz formula, by substitution of <w and e, 

 is equivalent to the crystallographic axial ratio. The agreement 

 is very good for a number of organic substances, but fails in 

 some cases, while for zircon and xenotime the ratio of the 

 " refractions " is equal to the axial ratio multiplied by 3/2. 

 From this, certain deductions concerning the spacing of the 

 atoms are made. 



W. H. McNairn (Trans. Roy. Can. Inst. 11, 231, 1916, 

 Amer. Min. 3, 138, 191 8) has investigated the origin and growth 

 of etch figures on certain monoclinic minerals, such as spodu- 

 mene, diopside, and colemanite. The location and distribution 

 of the etching pits is not due to chance, but bears some relation 

 to the molecular structure. 



A. P. Honess (Amer. Jour. Sci. (4) 45, 201, 191 8) has made 

 an interesting study of the etch figures of crystals belonging 

 to the dihexagonal alternating class. The materials used were 

 the rhombohedral carbonates, calcite being the subject of 

 investigation. Different solvents gave different types of etch- 

 pits so far as shape is concerned, while the tendency for the 

 formation of pits varied in different crystal faces. For 

 example, with hydrochloric acid, pits formed first on (10I1), 

 then on (10I0) and (1120), while they did not appear on the 



