The 400th anniversary of the birth of William Harvey.

William Harvey's discovery of the circulation of the blood is possibly the most famous of all scientific discoveries, and the fourth centenary of the birth of its author is as important as any centenary celebrations. We now can celebrate the wonderful advances in physiology, medicine, and surgery which have developed from it, but it must be remembered that for two hundred years it made no difference to any of these fields of activity. And yet, it was appreciated that it had been of profound importance. What it did at the time was this: it gave an actual, comprehensible demonstration of the scientific method of collecting observations, framing a provisional hypothesis to explain them, and testing the hypothesis by experiment. This scientific attitude has always been largely attributed to Francis Bacon, but wrongly: what he propounded was the collection of information on a large scale, and the consideration of it by a group of 'Interpreters', who just sat and thought. Bacon's idea of an experiment was one which answered the question: 'I wonder what would happen if ... ?' not whether it would confirm or disprove a hypothesis. But Harvey had clearly in mind, acted on, and described the modem method of scientific inquiry, and it was the direct effect of the 'De Motu Cordis' which stimulated the group of research workers in the College of Physicians, headed by Glisson, which was one of the formative influences in what became the Royal Society. It was such a transparently successful piece of work, so obviously imitable, that its effect can hardly be exaggerated. Moreover, it was widely disseminated, and became generally known in the 1620's, and in his own lifetime Harvey had the satisfaction of knowing that it had been generally accepted, except in France, where English work has never been popular. There were two subsidiary aspects of Harvey's method which had great influence: it was the first physiological experiment which employed numerical proofs, it finally demolished the mediaeval beliefs that the