1. EinsteinA., 1971, in Born, I. (trans.), The Born Einstein Letters, Macmillan Press, London, 29 April 1924, correspondence.
2. BohrN., 1949, in SchilppP. (ed.), Albert Einstein, Philosopher-Scientist, Library of Living Philosophers, Evanston, IL, p. 223.
3. MehraJ., 1975, The Solvay Conferences on Physics, D. Reidel, Dordrecht, pp. xvii and 146.
4. Witmer, E. E., 1966, Am. J. Phys. 35, 40?52.
5. Witmer, E. E., 1968, Am. J. Phys. 36, 277.