1. I. Newton,Principia (University of California Press, Cajori edition, 1960).
2. G. Berkeley,A Treatise Concerning the Principles of Human Knowledge, Sec. 110-117 (1710);
3. De Motu, Sec. 52-65 (1721);
4. The Works of George Berkeley (Clarendon, Oxford, 1901).
5. K. R. Popper,Br. J. Phil. Sci. 4, 26 (1953).