A major activity among geometers in the 3rd century bce was the development of geometric approaches in the study of the physical sciences—specifically, optics, mechanics, and astronomy. In each case the aim was to formulate the basic concepts and principles in terms of geometric and numerical quantities and then to derive the fundamental phenomena of the field by geometric constructions and proofs. In optics, Euclid’s textbook (called the Optics) set the precedent. Euclid postulated visual rays to be straight lines, and he defined the apparent size of an object in terms of the angle formed by the rays drawn from ...(100 of 41449 words)