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Light is the external physical cause of the sensation called sight. The earliest investigations as to the nature and behaviour of light were most probably made by the ancient Egyptians. Their work was followed by that of the ancient Greeks. Pythagoras and his followers (540 b.c.) formulated the theory that images formed in the eye were emanations from objects. The opposite view was taken by Empedocles and his followers (444 b.c.), who considered that the eye was endowed with the qualities of an octopus; the eye was supposed to project large numbers of tentacles which seized an object and caused it to be illuminated. Plato (430 b.c.) tried to combine the two theories, and explained light as the phenomenon caused by the collision and
“neutralisation” of emanations from both the eye and the object. It is believed that Plato's school enunciated two of the fundamental laws of light, that light travels in straight lines, that light is reflected in such a way that the angle of incidence is equal to the angle of reflection. Aristotle and his disciples (384 b.c.), however, maintained that light was not a material emission from any source but a mere quality of a medium called the "pellucid" Archimedes (287 b.c.) is said to have constructed huge mirrors with which he used the sun's rays to set fire to the Roman fleet at Syracuse (212 b.c.). The first mention of refraction, that is the bending of light when it leaves one transparent medium and enters another, was due to Ptolemy (a.d. 100)