Boussingault. Chemist and agriculturist

each problem developed, for, as Keele says, "the movement of Leonardo's mind through his life constituted a continuum". Before embarking on his analysis of Leonardo's perception and understanding of the anatomy and physiology of these aspects of Man and Machine, however, Keele considers the general principles of Leonardo's physics in a succinct discussion of his theories of the four elements and the four powers. "It is not easy to put ourselves into Leonardo's world", he writes, because the preconceptions with which Leonardo was brought up are very different from those accepted in post-Newtonian physics. In a remarkable extended analogy, Leonardo himself showed that he followed the medieval summation of classical, principally Aristotelian, and later thought in identifying the microcosm of Man with the macrocosm of Earth. Both the macrocosm and the microcosm are composed of the four elements, earth, water, air, and fire; and in parallel, the elements of earth and man are controlled by the four Powers of Nature, movement, weight, force, and percussion. Leonardo explained all the forms and forces of Man the microcosm as best he could in terms of these two simple and coherent quartets, and it is fundamentally important both to Leonardo and to Keele that the reader should comprehend this basis of Leonardo's physics and understanding of the physical world. In his Epilogue, Keele ties together the many threads he has pursued through this volume, which, although large, is nonetheless of necessity only an abbreviated account of Leonardo's entire scientific output. "To do Leonardo's work justice," Keele writes, "every chapter should be expanded into a book." It is an immense enterprise to produce a synopsis of such clarity and depth from so huge a corpus of surviving notes and sketches. Dr Keele has here made an important contribution not only to the history of medicine but also to the history of art, for he illustrates many little-known sketches alongside celebrated Leonardo drawings, and offers insights into the nature of Leonardo's mind and thought which the student of his paintings and drawings will do well to take in. For, in Leonardo's view, painting "explains the causes of Nature's manifestations as compelled by her laws": without the brilliance of draughtmanship which Leonardo displayed in all the drawings reproduced in this book he could not have started to discuss constructively most of the manifold problems in the science of Nature and Man that he investigated, because the …