 In his De visione stellarum Oresme departs from the standard view of earlier authors in optics such as Ptolemy (2nd century), Ibn al-Haytham (965–c. 1040), Roger Bacon (c. 1214–c. 1292), and Witelo (c. 1230/35–after 1275), who all held that refraction can only occur at the interface of two media of differing densities and thus would not take place in a single medium of uniformly varying density. He states – more than 300 years before Robert Hooke (1635–1703) and Newton – that atmospheric refraction occurs along a curve and proposes to approximate the curved path of a ray of light in a medium of uniformly varying density, in this case the atmosphere, by an infinite series of line segments each representing a single refraction (Burton 2007, 33–64).