1. A. Johannsen. "Manual of Petrographic Methods." New York, 1918, pp. 256-271.
2. J.M. Preston. "Modern Textile Microscopy." London, 1933, pp. 251-254.
3. R.D. Butler. Loc. cit (1), pp. 388-390.
4. E.R. Schwarz. "Textiles and the Microscope." New York, 1934, pp. 226-227.