1. I. M. Dalla-Valle, Micromeritics, Pitman, New-York, London, 1948, p. 20, Table 2.
2. Benford, Schwarz, Lloyd, J. Opt. Soc. Am.,38, 964 (1948).
3. Brumberg—Pekermann, Dokladi Akademii Nauk SzSzSzR.61, 43., 6 (1948).
4. Benford, J. Opt. Soc. Am.,36, 524 (1946).