1. K. S. Krishnan,Phil. Mag., 1925,50, 697.
2. K. S. Krishnan and A. Sircar,Ind. Jour. Phys., 1931,6, 193.
3. A. F. Turner,Inaugural Dessertation, Berlin University, 1935.
4. S. M. Mitra,Zeits. f. Phys., 1935,96, 29.
5. I. Ramakrishna Rao,Ind. Jour. Phys., 1927,2, 61; S. Ramachandra Rao,Ind. Jour. Phys., 1928,3, 1; R. S. Krishnan,Proc. Ind. Acad. Sci., A, 1936,3, 126.