The 'revolution in science' of this book concerns the natural sciences, that is, knowledge of the external world which we now presume to exist independently of man -- though in the recent past the close relationship between nature and man was universally held to be one of the best reasons for studying nature -- including in this the human body, which can be investigated objectively and which has long been compared with the bodies of animals. I shall not here consider either the sciences of mind and personality, or those of society, such as anthropology and economics. Considering science as knowledge means following the activities and writings of learned men: philosophers and mathematicians in the earlier centuries, astronomers, naturalists and chemists as they began to be called in the later ones. I shall not, in general, be analysing folkbeliefs (even though a good many of these were also current among some learned men, belief in astrology or witchcraft, for example) nor seeking to establish what knowledge of nature may have been, at least implicitly, expressed in the craftsman's command over living things and natural materials. Such topics have been investigated and are worthy of investigation, but lie apart from the literate and academic level which this book seeks to pursue. Nor is it merely snobbish to pursue the academic and neglect the popular. It is no modern aberration for the ordinary citizen's image of the world he inhabits to be a popularization of that held by academic pundits; most of Shakespeare's science can be traced back to perfectly good classical and medieval antecedents. It is no accident that the popular knowledge of his day about sex and reproduction was derived from a work entitled Aristotle's Masterpiece, or that seventeenth-century popular astrology still bore marks of its origins among the Babylonian mathematicians. Some pieces of scientific knowledge have grown upwards from the soil -- Jenner's discovery of vaccination is perhaps the most famous of them -- but an incomparably larger number of folk-beliefs have sedimented down from above. Moreover, it is in the learned works of a society that the historian finds its view of nature -- even its errors and superstitions -- most clearly and cogently presented. Indeed, just as today we could not discover from Samoans what it was like to grow up in Samoa fifty years ago but only learn this from the anthropological studies of Margaret Mead, so we can usually only discover what ordinary people . . .