In 1574, Taqi al-Din (1526–1585) wrote the last major Arabic work on optics, entitled "Book of the Light of the Pupil of Vision and the Light of the Truth of the Sights", which contains experimental investigations in three volumes on vision, the light's reflection, and the light's refraction. The book deals with the structure of light, its diffusion and global refraction, and the relation between light and colour. In the first volume, he discusses "the nature of light, the source of light, the nature of the propagation of light, the formation of sight, and the effect of light on the eye and sight". In the second volume, he provides "experimental proof of the specular reflection of accidental as well as essential light, a complete formulation of the laws of reflection, and a description of the construction and use of a copper instrument for measuring reflections from plane, spherical, cylindrical, and conical mirrors, whether convex or concave." The third volume "analyses the important question of the variations light undergoes while traveling in mediums having different densities, i.e. the nature of refracted light, the formation of refraction, the nature of images formed by refracted light."