IN such elementary text-books on geometrical optics as I have consulted it has always seemed to me that the writers have found a difficulty in presenting a precise direct proof of the theorem that ...

Refraction close refractionProcess by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens. of ...

Newton’s experiment remains almost insultingly simple. Sunlight, a darkened room, a glass prism. The conclusion was unavoidable. Colour belonged to light itself. The prism merely made it visible.