How did Isaac Newton show that white light contains a mixture of colors?

Isaac Newton demonstrated that white light is a heterogeneous mixture of colors through a series of experiments conducted in 1665 and 1666. Contrary to the prevailing ancient theory—which suggested that white light was pure and that colors were merely modifications of it—Newton proposed that white light is a complex mixture that can be analyzed into its simple components.1

By projecting a narrow beam of light through a prism onto the wall of a darkened chamber, Newton observed that the light dispersed into a spectrum of colors. He concluded that this occurred because individual rays of light possess immutable properties and refract at distinct angles when passing through the prism. This process, known as chromatic dispersion, revealed that white light is composed of these various colored rays, which excite different color sensations when they strike the retina of the eye. This discovery fundamentally shifted the understanding of optics and led Newton to develop the reflecting telescope to avoid the chromatic aberration inherent in lenses.12