1474 



Journal of Applied Microscopy 



NOTES ON RECENT MINERALOGICAL 

 LITERATURE. 



Alfred J. Moses and Lea McI. Luquer. 



Books and reprints for review should be sent to Alfred J. Moses, Columbia University, 



New York. N. Y. 



Viola, C. Ueber optische Erscheinung am 

 Quarz und am Turmalin von Elba. Zeit. f. 

 Kryst. 32: 551-560, 1899. 



Wulfung, E. A. Ueber die Lichtbewegung im 

 Turmalin Centralblatt. f. Min. Geol. u. 

 Palaen. Pp. 299-302, 1901. 



Viola claims that the indices of refrac- 

 tion for quartz can be determined from 

 a cut plate by the Abbe refractometer 

 with exactitude to the fifth decimal 

 place. From hoo sections cut from 

 the same crystal of quartz, one parallel, the other perpendicular to the optic axis, 

 he obtained for the ordinary ray with sodium light : 

 00 (transmission parallel axis) 1.54426. 

 CsD (transmission perpendicular to axis) 1.54442. 

 That is, a difference of 0.0U(I16. 

 From which he concludes that the wave surface consists of two rotation 

 ellipsoids, and that the Fresnel theory is not here available. 



In tourmaline, using, however, the prism method, but using two different 

 prisms from the same crystal, he obtains for the ordinary index in Elba tour- 

 malines with sodium light : 



Transmission 



Parallel 



axis. 



Yellow crystals, - - 1.6494 



Colorless crystals. 

 Green crystals, 



Wiilfing objects to the conclusions of Viola, pointing out that in the case of 

 quartz, in spite of great care in observation and in construction of the apparatus, 

 -L., it is not possible to claim absolute freedom from error to the 

 fourth decimal. In case of tourmaline, he points out the 

 well known variation in composition in different portions of 

 same crystal. To avoid this he prepared a single four-sided 

 pyramid, so that both directions of transmission were through 

 the same material, as in the figure, the dotted lines repre- 

 senting the portion of the tourmaline that was ground away. 

 With such pyramids he obtained for oj : 



1.6425 

 1.6479 



Transmission 



Perpendicular 



axis 



1.6482 

 1.6402 

 1.6503 



Difference. 



0.0012 

 0.0023 

 0.0024 



That is, the greatest difference was yV to -,}-^ that obtained by Viola, and 

 indicate that, at least for tourmaline, the Fresnel law holds. a. j. m. 



