1. R. Ward, The Life of Henry More, Vols. I and II, Springer (2000)
2. C.E. Hinton, Speculations on the Fourth Dimension, Dover (180)
3. A fascinating account of the early days of Kaluza-Klein theories is given by O. Raifeartaigh, hep-ph/9810524 (1998). See also The Dawning of Gauge Theory by the same author, Princeton U. Press (1997)
4. T. Kaluza, Sitz. Preuss. Akad. Wiss. Berlin (Math.Phys.) (1921) 966–972
5. O. Klein, Z. Phys. 37 (1926) 895–906