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 ...

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.

Sunlight may be the bright, warming glow that heats and powers the Earth, but it's so much more than that. If you pass sunlight through a prism, you can see how it's actually composed of all the ...