In Nature in 1971, volume 233, page 357, W. H. Brock reviewed a book by Robert Fox, The Caloric Theory of Gases from Lavoisier to Regnault, published by Oxford U. The reviewer begins with this comment of Edward Frankland: “it is by no means necessary that a theory should be absolutely true in order to be a great help to the progress of science." Very nice quote. It relates to the epistemology of scientific knowledge as well as the historical progress of science. No source is given for the quote. Do you know the provenance of the quote?