Newton’s first discoveries dealt with optics, most of which were made during the plague years. He reached the conclusion that white light is not a simple, uniform thing. This is what the philosophers since Aristotle had believed. The old theory said that all rays of white light striking the prism at the same angle would be refracted equally. Newton found that white light is really a mixture of many different types of rays. These rays are refracted at slightly different angles. Each different type of ray is responsible for producing a given spectral color. Another experiment confirmed his theory. Newton selected the narrow band of light form one color of the spectrum. When it was sent through a second prism and observed the ray was the same length. This proved that all the rays of one color are refracted at the same angle.