THE Oxford-Paris Connection of Optics and the Rainbow: Grosseteste's De iride, Pseudo-Oresme's Inter omnes impressiones and Bacon's Perspectiva in Paris, BNF, lat. 7434

In this paper I present some details concerning the study of geometrical optics (perspectiva) at Oxford in its application of the theory of the rainbow according to Robert Grosseteste’s De iride and to an anonymous and hitherto unknown treatise on the rainbow by the incipit Inter omnes impressiones, wrongly attributed in the past to Nicole Oresme. These two texts plus an anonymous De generatione iridis form a textual unit collocated after Bacon’s Perspectiva in manuscript Paris, BnF, 7434, which belonged to and was annotated by Peter of Limoges, thereby showing their early diffusion in Paris. The first section of the paper proposes a summary of Bacon’s main achievements in the science of optics and how they were grounded on Grosseteste’s elaboration of perspectiva, which is examined in the second section in the light of the copy of Grosseteste’s De iride transmitted in the Parisian manuscript. This version allows several improvements of the deceptive edition by Ludwig Baur (1912), and permits the clarification of how Grosseteste introduced the very term perspectiva in the context of the Aristotelian theory of the subalternation of sciences. The third section proposes a summary of the Inter omnes impressiones, known and largely quoted by Oresme in his early version of the Questions on Meteorology. The Inter omnes impressiones uses Grosseteste’s theories of rainbow as being due to sunlight refraction and of colour as incorporation of light – the latter was adopted also in the De generatione iridis – but develops new issues as regards the role of the single raindrops, the importance of the angular location of the observer and the idea of the spirituality of colours in the medium, which were central also for Bacon and Oresmes’ theories on perspective. and the rainbow.