The inclusion in this volume of William Whewell, the historian and philosopher of science, may require some comment. Unlike Isaac Newton, Charles Darwin, or James Clerk Maxwell, he was not a major scientific discoverer and does not feature in any list of great scientific minds. On the other hand, however, as a person who lived in Cambridge from 1812 until his death in 1866, Whewell's connection with that place was arguably more continuing and deeper than that of many others who began their scientific lives there. I shall begin with this last point and then return to Whewell's contribution to the historical and philosophical understanding of science, one that fully justifies his treatment in this book.