Biographical dictionary of the history of technology

philosophies to discern how the belief in this effect was achieved. To tell more, however, would be to spoil a good story. The chapters on the other machines are equally well done if having slightly less of the flavour of the detective story. In two chapters the authors desert their genre and pursue the precursors of modern devices: graphs and photographic depictions. Both of these chapters are informative and theoretically interesting, especially the latter, which includes a useful discussion of how photographic (and other) images in the past were regarded as either natural (realist) or conventional representations. According to which approach was adopted unusual images could be designated as either unnatural distortions of nature or extensions of vision. Such a decision has had important consequences in the history of science as in the debate over Galileo's telescope. Let this volume be a lesson to historians of medicine and let us see contextual studies not just of odd ideas but of odd machines: Perkin's tractors or the Pulvermacher Belt, for instance.