1. E. Mach:The Science of Mechanics (La Salle, Ill., 1960).
2. The Leibniz-Clark Correspondence, edited byH. G. Alexander (Manchester, 1956).
3. G. Berkeley:The Principles of Human Knowledge (1710);
4. Concerning Motion (De Motu) (1721).
5. J. Ehlers: inThe Physicist's Conception of Nature, edited byJ. Mehra (1973), p. 71.