1. Milne, E. A., Proc. Roy. Soc., A, 156, 69 (1936) and Quart. J. Math. (Oxford), 8, 22 (1937).
2. Whitrow, G. J., Quart. J. Math. (Oxford), 6, 249 (1935).
3. Milne, E. A., Proc. Roy. Soc., A, 158, 327 (1937). There are certain departures from the Einstein mechanics for speeds v approaching c.
4. Milne, E. A., Proc. Roy. Soc., A, 165, 343 (1938).
5. Whitrow, G. J., Quart. J. Math. (Oxford), 7, 271 (1936).