Optics in Ancient China

The early contributions of ancient China to optics predate those of Euclid, but are little known in the west. During the Warring States period, 2400 years ago in China, Mo Zi, a philosopher, thinker and scientist, stated explicitly the concepts of linear optics: the straight line propagation of light, reflection of light by planar, concave and convex mirrors, and the pinhole camera. Refraction of light was also discovered then, and the refractive index of water was measured to be 1.25, which is very close to the modern value of 1.33. These are recorded in the Book of Mo Zi. In the early Western Han Dynasty, Liu An, King of Huai-Nan, also compiled several works, where novel optical devices are …