1. Weyl, H. (1917).Ann. d. Physik,54, 117; (1919).ibid.,59, 185.
2. Levi-Civita, T. (1917?1919).Atti. Accad. Nazl. Lincei,26,27, 28, numerous short articles.
3. For a particularly lucid derivation, see Synge, J. (1958).Relativity: The General Theory (North Holland, Amsterdam), Chapter VIII.
4. Partially summarised in Darmois, M. (1927).Les Equations de la Gravitation Einsteinienne (Gauthier-Villars, Paris).
5. See also Wilson, W. (1920).Phil. Mag.,40, 703, and Bach, R. and Weyl, H. (1922).Math. Zeit.,13, 134.