The spectrum of sunlight is a familiar sight, particularly after a rainstorm; tiny particles of water suspended in the air will split the Sun's white light into a rainbow. Anyone who has played with a prism has probably duplicated this phenomenon. The first person to examine the color spectrum in this way was the renowned English physicist and mathematician Isaac Newton, and it was he who provided the first insight into the composite nature of light.

Newton performed his optical experiments between 1665 and 1666, and they are described in detail in letters compiled and published in 1672 under the title Philosophical Transactions. Though his previous work had primarily been in mathematics and the development of calculus, he was apparently inspired by the research of Robert Boyle and Johannes Kepler to examine the nature of light. Newton obtained a beam of light by allowing sunlight to pass through a...