ALTERNATIVES TO THE CORPUSCULAR THEORY

Some of Newton’s colleagues thought he painted an overly simplistic picture of the nature of light, so they set out to find alternative models. Christian Huygens, a Dutch physicist fond of optics, was one of the first to suggest that visible light is a wave disturbance, like the ripples on a pond or the vibrations of a violin string. Today, even laypeople speak of light waves as if the two words go together. To scientists in the 1600s, however, the connection was not obvious. Huygens kept at his research and showed that light waves interfere with each other in the same way as waves on water and in the same way as waves from musical instruments. This explains the ripples or concentric rings seen around images in high-powered optical instruments.
The bending of light rays at the surface of a lake or pool is consistent with the wave theory. When a light beam strikes the surface, the beam is bent at an angle (Fig. 1). The extent of the bending depends on the angle at which the wavefronts strike the surface. Wavefronts parallel to the boundary are not bent. Wavefronts striking the water surface at a large enough angle from within the water do not pass through the surface boundary but are reflected instead.

Fig. 1. Light waves change speed and wavelength when they strike a boundary between media having different indices of refraction.