This project focused on scientific observation, a topic that had previously never been studied in a manner sensitive to actors’ categories; the few scholars who have written on this topic have treated observation anachronistically, assuming that it was part of an undifferentiated, experience-based study of nature. In fact, there was a clear distinction between the sciences of experience (experientia/experimentum) and those of observation (observatio). The former—notably the Aristotelian sciences, as well as medicine, alchemy, and astronomy—invoked experience in the sense of trial or test: a punctual intervention intended to test the truth of a statement (e.g., that the cries of migrating birds are cries of pain, rather than attempts at communication), the accuracy of a planetary table, or the efficacity of a remedy or procedure. In contrast, the sciences of observation—astrology (the part of astronomy dealing with the terrestrial effects of changes in the heavens), agriculture, and navigation) were organized around the idea of watching and waiting, the patient noting and recording of longtime cyclical phenomena in order to determine patterns and correlations, e.g., among particular planetary configurations, weather conditions, political events, or optimum times to harvest or plant. Although medieval writers typically attributed observation to the ancient founders of the sciences in question (the Babylonians, the Egyptians, the pre-Hippocratics), there is evidence of medieval programs of observation related to monastic timekeeping and, beginning in the thirteenth century, weather science; individual observers attempted to lay the foundations for a science of weather prediction based on the positions of celestial bodies, by making daily records of the weather in the margins of manuscript and, eventually, printed ephemerides.