Demonstrative induction,old and new evidence and the accuracy of the electrostatic inverse square law

Maxwell claimed that the electrostatic inverse square law could be deduced from Cavendish's spherical condenser experiment. This is true only if the accuracy claims made by Cavendish and Maxwell are ignored, for both used the inverse square law as a premise in their analyses of experimental accuracy. By so doing, they assumed the very law the accuracy of which the Cavendish experiment was supposed to test. This paper attempts to make rational sense of this apparently circular procedure and to relate it to some variants of traditional problems concerning old and new evidence.My interest in demonstrative induction developed as the result of being given the opportunity by Joseph Pitt to comment on an earlier version of John Norton's Science and Certainty (1994) at a conference held at the Virginia Polytechnic Institute and State University. I want to thank Joe and John for much stimulating discussion and John specifically for sharing his work on demonstrative induction with me. My gratitude also goes to the National Science Foundation (DIR-8920699) and Ohio State University for providing funding for a larger project of which this paper forms a part.