Grosseteste’s short works in optics, particularly his De lineis-De natura locorum and De iride, assign great importance to mathematics in scientific explanations of the physical world. This is because natural agents act upon the senses or matter through the multiplication of their ‘‘species,’’ or rays, according to the agent’s distance, the angle of their incidence, and the sphere or cone resulting from their multiplication, a view later developed by Roger Bacon (Hackett in McEvoy 1995). The geometrical attitude of Grosseteste’s physics illustrates the basic assumptions of his theory of science, developed in his Commentary on Posterior Analytics (Rossi in McEvoy 1995). First, there is a double inquiring path, called ‘‘resolution’’ and ‘‘composition.’’ Resolution or analysis starts with observations to arrive at universal laws, while composition or synthesis moves from universal laws to infer particular facts. Both ways are verified through experimentation and a clear distinction between why (propter quid) and how (quia) a fact happens. Scientific demonstration of how a fact happens implies the move from effects to cause; conversely, the demonstration of why it happens moves from cause to effects. Secondly, the Aristotelian theory of the subalternation of the sciences implies that the principles of optics are conclusions in geometry. Thus, mathematics is the highest and propter quid science, being based first on axioms, and every natural science ultimately depends on it (Laird 1987). This methodological principle accompanies the theory that light gives the universe both its physical and its mathematical structure, being its first form and acting according to linear rays and geometrical figures. Thirdly, although the human intellect does not rely on the senses in its proper operation, but contemplates the exemplar forms through a divine illumination, in the present life repeated sense experience moves reason to formulate an ‘‘experimental’’ universal principle. The universale complexum experimentale is a sort of universal proposition which sets forth the links of causality between two events (Rossi 2008). These three basic principles have nourished Grosseteste’s modern reputation as the beginner of the western experimental method (Crombie 1953). Grosseteste’s claims on controlled experiment have been more rightly linked to everyday observation (Marrone 1986; Hackett in Mc Evoy 1995), but even in his works on optics Grosseteste fails to apply them. This is true ofhis On the Rainbow, though in this work he is the first in medieval science to introduce the law of refraction as the main cause of the rainbow (Eastwood 1989). Surely, Grosseteste’s emphasis on mathematics was his chief legacy to natural philosophy in fourteenth-century Oxford.
World History
