Philosophiæ Naturalis Principia Mathematica
While it was difficult for many (such as Hooke) to conceive of the enormous speed of light, acceptance of Rømer's idea suffered a second handicap in that they were based on Kepler's model of the planets orbiting the Sun in elliptical orbits. While Kepler's model had widespread acceptance by the late seventeenth century, it was still considered sufficiently controversial for Newton to spend several pages discussing the observational evidence in favour in his "Philosophiæ Naturalis Principia Mathematica" (1687).