ABSTRACT
During the Middle Ages, no particular incompatibi l i ty had been discerned between, on the one hand, Aristotle's doctrine of the concentric arrangement of the spheres of the four elements (earth, water, air and fire) together with that of his fifth essence,' and, on the other hand, the principles of optics as laid down in botli the Optica of Euclid (fl. 300 BC)-' and in the Optica of Claudius Ptolemy (90 AD-168 AD).? Both these texts were translated into Latin in the twelfth century.4
