During 1971 two new books were added to the immense amount of published work on Wren’s architecture, one written by Margaret Whinney and the other by Kerry Downes. This evidence of a continuing interest in the critical appraisal of Wren’s buildings seems to invite a contribution from the neglected study of his natural philosophy. A number of articles have been published on various aspects of Wren’s ‘scientific work’, but we are still without a general critical account and, as a result, this valuable source of knowledge about Wren has remained largely untapped. The present article can only be a beginning, but it will aim at an understanding between two separate academic disciplines, the histories of science and of architecture. As such it risks censure by either or by both. Wren’s natural philosophy is more properly the subject of a book than of an article and we must be extremely selective, drawing on examples from his work which illustrate general conclusions. On the other hand there is, of course, a great deal of published material on Wren the architect. Any attempt to summarize the ‘results’ of this work, by giving what purport to be representative conclusions, will seem naive to anyone who has studied the changing expression of Wren’s remarkable talent. In order to minimize these difficulties, we will concentrate on the solution of one problem, namely the interpretation of Wren’s theory of beauty, as it has been preserved in his first tract on architecture. This is a single problem, but I will try to show that it is also a central one, having implications which involve our whole approach to Wren’s work. It also seems to raise more general questions, concerning the historiography of the history of architecture.