WRIGHT: A NEW CRYSTAL-GRINDING GONIOMETER 



35 



CRYSTALLOGRAPHY. — A new crystal-grinding goniometer. 

 Fred. E. Wright, Geophysical Laboratory. 



In the measurement of the change of crystallographical and 

 optical properties of crystals with change of temperature or of 

 pressure it is essential that the crystal faces be flat and correctly 

 located; also that the optical sections and prisms be accurately 

 oriented and ground. Natural crystals with faces sufficiently 

 perfect for such work are exceedingly rare and the observer is 



Fig. 1 



usually forced to regrind and polish certain of the faces and often 

 to add new faces of definite orientation. This postulates an in- 

 strument of precision for the purpose. Several crystal-grinding 

 goniometers have been described heretofore/ and of these the 



iWolz, M., Jahrb. f. Min., 2: 243-246. 1888. 



Fuess, R., Jahrb. f. Min., 2: 181-185. 1889. 



Wulfing, E. A., Zeitschr. f. Kryst., 17: 445-459. 1890; Jahrb. f. Min., 2: 

 1-22. 1901. 



Tutton, A. E. H., Crystalline Structure and Chemical Constitution, 25-35: 

 1910; Phil. Trans., A, 185: 887. 1895; 192: 457. 1899; Proc. Roy. Soc. 67: 324. 

 1895. 



Stober, F., Bull. Ac. Beige, (3) 33: 843-858. 1897. 



Goldschmidt, V., Zeitschr. Kryst., 51: 358. 1912. 



Wulff, G., Zeitschr. Kryst., 36: 22. 1902; 50: 14-16. 1913. 



