The angle of refraction depends on the speed at which light travels through a medium. People have noticed the phenomenon of refraction throughout history. But the first to discover the law of refraction was Willebrord Snell (1580-1626), a Dutch mathematician. The refractive index of water to the orange sodium-vapor light emitted by streetlamps on highways is 1.33. The refractive index of water to violet, which has a short wavelength, is nearly 1.34. To red light, which has a long wavelength, the refractive index of water is almost 1.32.