This section covers Newton's corpuscular model and its explanations of reflection, refraction and the speed of light in denser media.
Light as corpuscles
Newton treated light as a stream of minute particles called corpuscles, emitted by luminous objects.
The model could account for reflection, refraction and dispersion, but it did not provide a satisfactory explanation for diffraction.
Reflection
Newton supposed that a short-range repulsive interaction with the surface reverses the component of a corpuscle's velocity perpendicular to the surface. Its velocity component parallel to the surface is unchanged.
Refraction
Near a denser material, Newton proposed a resultant attraction towards the material. The perpendicular velocity component therefore increases while the parallel component remains constant, turning the path towards the normal.
This explanation leads to an important prediction: the total velocity of a corpuscle increases in the denser medium. Newton's theory therefore predicts that light travels faster in water than in air.
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