1. D. Z. Freedman and P. van Nieuwenhuizen, “Supergravity and the Unification of the Laws of Physics,” Sci. Am. 238, 126 (1978).
2. Charles Babbage, The Ninth Bridgewater Treatise, 2nd ed. (John Murray, London, 1838), p. 179.
3. Today Mossotti is almost exclusively known for his contribution to the theory of the atomic polarizability of dielectrics embodied in the “Claussius-Mossotti” equation.
4. There are a number of works that deal with the germane issues in physics in the 19th century. Particularly helpful are E. Whittaker, A History of the Theories of Aether and Electricity, 2 Vols. (Thomas Nelson and Sons, London, 1951 and 1953)
5. M. B. Hesse, Forces and Fields (New York Philosophical Library, 1961)