1. Lavinir, A.: Bull. Soc. Fr. Mineral. Cristallogr. 17 (1894) 153.
2. Mandell, W.: Proc. R. Soc. London, Ser. A 121 (1928) 130.
3. Astbury, W.T.: p. 353 in [30Was] Washburn, E.W. (ed.): International Critical Tables, Vol. 7, New York: McGraw-Hill Book Co. Inc., 1930.
4. Washburn, E.W. (ed.): International Critical Tables, Vol. 7, New York: McGraw-Hill Book Co. Inc., 1930.
5. Bloomenthal, S.: Physics 4 (1933) 172.