1. The gnomonic projection, its properties and uses to the crystallographer, will be found in V. Goldschmidt, ‘Ueber Projektion u. Krystallberechnung’ (1887), or in H. E. Boeke, ‘Die Gnomonische Projektion’ (1913). A simple discussion is given by C. Palache in Am. Mineralogist 5 (1920) 67.
2. C. T. Ulrey, Phys. Rev. (2) 11 (1918) 401.
3. A. W. Hull, Proc. Nat. Acad. Sci. 2 (1916) 265.
4. C. T. Ulrey, op. cit.
5. C. G. Barkla and G. H. Martyn, Phil. Mag. 25 (1913) 296.