Galileo, Hobbes, and the Circle of Perfection

may be as much as half a dozen degrees smaller than the one which Descartes had measured and calculated.28 This fact led Young to question the whole Cartesian theory of the rainbow, with the result that the geometrical explanation gave way to a physical theory based upon the wave theory of light.29 So thoroughly did Airy and others 30 investigate the rainbow problem from the point of view of interference that, whereas Descartes once confidently calculated the size of the rainbow from the geometry of a spherical drop, it now became possible, inversely, to calculate from the observed radius and characteristics of a given rainbow,31 the size of the drops producing it! Had Descartes been a better historian of science, he would have realized that his work was neither the first nor the last significant contribution on the radius of the rainbow.