OpticksIsaac Newton

Newton's second great book, published in 1704, twenty years after he had first presented its results to the Royal Society. Unlike the Principia, the Opticks is written in English, in the plain language of experiment, and addressed to a general readership. It reports Newton's work on light, color, and the laws governing them.

The central experiment is the prism. A beam of white light, passed through a glass prism in a darkened room, spreads into a band of colors. Newton shows that each color refracts at its own fixed angle, that once a single color is isolated no further prism can change it, and that recombining the colors restores white light. Colors are therefore not modifications produced by the glass, as his predecessors had held, but original components of white light itself.

From this ground the book develops the law of refraction, the formation of the rainbow, the colors of thin films, diffraction at the edges of bodies, and the construction of the reflecting telescope. The treatise closes with a series of Queries in which Newton speculates about the corpuscular nature of light, the action of bodies on each other at a distance, and the relation of matter to spirit.

The Opticks shaped experimental physics for a century, its method of careful experiment and cautious inference standing as the model for Enlightenment natural philosophy.