This paper is concerned with the particular problems raised by observations of phenomena outside the common course of nature for their validation as knowledge. It examines to what extent the content of the reports and, in particular, their lack of intrinsic plausibility affected the methods used in their authentication and the assessment of testimony at the Royal Society in the first half of the eighteenth century. I show that literary strategies were usually necessary but not sufficient for the validation of (...) these kinds of observations. Next, I discuss why visual representations were especially useful in establishing the singularity of the observations, but I point out that their high costs and other restrictions meant that they were not so widespread. In contrast I show that, for a long period of time, testimony was used in the majority of the reports as the true stamp of authenticity. I note, however, that the Royal Society accepted reports by authors of varied social status, level of education and occupation, and I discuss some of the factors responsible for the complexity of the handling of testimony at the Society. I argue against Shapin that in the case of reports of extraordinary phenomena, the competence of the reporter and witnesses was often more important than their social status. The increasing role of expertise in the assessment of observations at the Society become especially apparent by the middle of the eighteenth century.Author Keywords: Authentication; Competence; Monstrous births; Singular; Testimony; Royal Society of London. (shrink)

While historians of the microscope currently consider that no programme of microscopy took place during the Enlightenment, the thesis challenges this view and aims at showing when and where microscopes were used as research tools. The focus of the inquiry is the research on microscopic animalcules and the relationship of European microscope making and practices of microscopy with topical trends of the industrial revolution, such as quantification. Three waves of research are characterised for the research on animalcules in the Enlightenment: (...) 1. seventeenth-century observations on animalcules crowned by Louis Joblot's 1718 works in the milieu of Paris Académie royale des sciences, 2. mid eighteenth-century observations and experiments on polyps and animalcules (Trembley, Baker and Hill) and, 3. between 1760 and 1790, OF Müller's establishment of the systematics of infusoria in Denmark and Germany. (shrink)