1. S. Bhagavantam,Ind. Jour. Phys., 1930,5, 35; C. S. Venkateswaran,Proc. Ind. Acad. Sci., 1937,4, 345.
2. Optik, Julius Springer, 1933.
3. Maxwell, Hendricks and Mosley,Jour. Chem. Phys., 1935,3, 699.
4. The value is taken fromLandolt Bornstein Tabellen and is due to Ewald.