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Newton's theory of light stated that a light travelled in a straight line as small particles. When these particles travelled in a medium, they experienced an attractive force with the particles of the surrounding medium. This attractive force was equal in all directions, and hence the particle travelled in a straight line. He extended this to explain refraction by saying that when light entered a denser medium, the particles would experience differing levels of attractive forces, as the denser medium would have more particles. This would lead it to bend towards/away from the normal.
However, in this case, how did he explain why different colours of light refracted at different angles?