It can not be shown then that there was bitter warfare between science and theology in the middle ages; nor, on the other hand, was science a handmaid at theology's beck and call. The two interests were beginning to separate, sometimes with a little friction, often with much caution on the part of science, yet on the whole with maintenance of friendly relations between them. Science was still somewhat under the wing of the church, but science was learning to use its own wings.
Having traced back the scientific spirit in western Christian Europe to the twelfth and thirteenth centuries rather than to the time of the Italian Renaissance, let us now examine some of the particular fields which it investigated.
Physics was studied now, and not merely along the theoretical lines of Aristotle's treatise. Further progress had been made among the Arabs in optics; and the subjects of vision, perspective, reflection and refraction were now better understood than in the time of Ptolemy. The men of the thirteenth century speedily absorbed these new ideas of the Arabs. Roger Bacon, it is true, while according due credit to the Arabs, gives us the impression that his Latin contemporaries were neglecting the subject of optics, and describes the formation of rainbows, and the characteristics of convex and concave mirrors, burning glasses and lenses by which the size of objects can be greatly magnified, or mirrors by which their numbers can be greatly multiplied, as if all these things were marvelous novelties. Bacon's own discussion of these matters is excellent, and in some details he corrects or adds to his Arabian authorities, but he does not do justice to his Christian contemporaries. At just about this time Witelo, a Pole who traveled in Italy, wrote an important treatise on optics in which he embodied the views of Alhazen, the leading Arabian authority, together with many additions from other writers and of his own. Moreover, the French "Romance of the Rose," probably written soon after Bacon's work, shows remarkable familiarity with all the things that he describes. Of rainbows it remarks that
Only he who's learned the rule
Of optics in some famous school
Can to his fellow men explain
How 'tis that from the sun they gain
Their glorious hues.
The author also mentions burning-glasses and various other sorts of mirrors, but he refers to all these as well-known scientific facts, and says that there are plenty of books about them. He also unmistakably describesglasses when he tells us that from optics one
... may learn the cause
Why mirrors, through some subtle laws
Have power to objects seen therein
(Atoms minute or letters thin)
To give appearance of fair size,