1. The measurement of visual sensations
2. Churcher B. G. King A. J. and Davies H. (1934). ` J. Inst. Elect. Eng. Lond. ' Oct.
3. Guild J. (1932). *Phys. and Opt. Soc. ' Discussion on Vision p. 60.
4. *J;Ham;Acoust. Soc. Amer.,',1932
5. Maxwell R. S. (1929). ` Brit. J. Psychol. ' vol. 20 p. 181.