 When medieval writers speak of knowing matters per experientiam (by experience), they are understanding the term experientia very broadly. The same may be said of the term experimentalis, so that the phrase scientia experimentalis should be translated as “experiential knowledge” rather than “experimental science.” Although Bacon’s scientia experimentalis did include practical procedures (experimenta), as were used in alchemy, as well as the use of instruments (as in the study of optics and astronomy), it also included simple observation as well as reliance on second-hand reports of dubious value. (We are still a long way from the motto of the seventeenth-century Royal Society: nullius in verba, “take no man’s word for it.”) Nor is there any consistent link with quantification. In only a few fields, such as astronomy, are the procedures employed by natural philosophers associated with careful measurement. In the century following Bacon’s work, we do find the development of what we may call “quantified concepts,” particularly in the study of local motion. We find this, in particular, in the work of the Oxford calculatores associated with Merton College, who are perhaps best known for their formulation of the “mean speed theorem.” This was the idea that 