1. Coker, E. G. and L. N. G. Filon, Photo-Elasticity, Cambridge University Press, 1931, pp. 374?381.
2. Ling, C. B. and P. S. Wang, C. B. Ling's Collected Papers, Institute of Mathematics, Academia Sinica, Taiwan, China (1963) 75.
3. Radkowski, P. P., Proc. of Second U.S. Congress of Appl. Mech. (1955) 277. An abstract appears in J. of Appl. Mech. 21 (1954) A-287.
4. Howland, R. C. J., Proc. of Cambridge Phil. Soc. 30 (1934) 315.
5. Ling, C. B., Quarterly of Appl. Math. 5 (1947) 168.