How did Isaac Newton use a prism to study white light?

Through experiments conducted in 1665 and 1666, Isaac Newton used a prism to challenge the prevailing belief that white light was simple and homogeneous. By projecting a narrow beam of light through a prism into a darkened chamber, he demonstrated that white light is actually a complex, heterogeneous mixture of rays.1

Newton observed that when this beam passed through the prism, it underwent refraction at distinct angles, causing the light to separate into a spectrum of colors. He concluded that these colors were not modifications of white light, but rather its fundamental components, each possessing immutable properties. This process of prismatic analysis revealed that the index of refraction varies with color, an effect known as chromatic dispersion.12

Because he believed this dispersion meant that lenses would always suffer from chromatic aberration, Newton applied his findings to invent the reflecting telescope, which uses mirrors to avoid the color distortion inherent in refracting glass.12