1. Cajori F., Sir Isaac Newton's Mathematical Principles of Natural Philosophy and his System of the World (Berkeley, 1947), 407. For an account of Newton's treatment of the problem of the lunar precession and of Clairaut's eventual solution of it, see Waff Craig B. “Clairaut and the motion of the lunar apse: The inverse square law undergoes a test”, chap. 16 in The general history of astronomy, vol. 2B, ed. by Taton R. and Wilson C. (Cambridge, 1995), 35–46.
2. A suggestion in the theory of Mercury
3. See Danby J. M. A., Fundamentals of celestial mechanics, 2nd edn (Richmond, Virginia, 1988), 62, equation (4.3.2).
4. The Relativity Effect in Planetary Motions