How did Newton explain why a prism bends light rays causing the colors to separate? We know today that light has wavelike properties. This explains why the rays are bent when they enter the prism. Light slows down when traveling through a medium, as the trough enters the prism before the crest, the bottom part of the wave slows down (before the top) and causes it to bend the ray, which results in the separation of colors, as each color has a different wavelength.
But as Newton believed that light is made of tiny corpuscles/particles, and didn't subscribe to the wave theory, how did he explain the science of refraction? Why does the prism bend the light ray? And more importantly how does white light get separated into different colors?
 A: Newton explained the refraction of light towards the normal on entering a 'denser' medium to be due to the corpuscles experiencing an attractive force directed normally towards the surface of the medium. When the corpuscle emerges into the less dense medium the normal force will cause its path to bend away from the normal. Presumably the blue corpuscles experience stronger forces than the red, so the blue light bends more.
It is, at least superficially, easy to see how the corpuscular theory leads to Snell's law. There is no force on the corpuscles parallel to the surface, so their velocity component parallel to the surface is unchanged, that is, with the usual notation,
$$v_1\sin \theta_1=v_2\sin \theta_2$$
That is
$$\frac{\sin \theta_1}{\sin \theta_2}=\frac{v_2}{v_1}$$
So we have Snell's law if we assume that $v_2/v_1$ is a constant for the media. But this seems to me to be an unnatural assumption for corpuscles, and as M Enns has explained, if $\frac{\sin \theta_1}{\sin \theta_2}>1$ (for example if medium 1 is air and medium 2 is water), direct time-and-distance measurements for light (Fizeau, Foucault c.1850) showed that $v_2<v_1$.
