Isaac Newton’s prism experiment showed that sunlight splits into colors when it passes through a glass prism. The familiar band is the visible spectrum, ranging continuously from red through orange, yellow, green, blue, and violet.
Newton performed his classic optical investigations in the 1660s and later described them in Opticks, published in 1704. He used a second prism to show that the colors were not created by the glass: a selected color remained that color rather than being split again into a new full spectrum.
The key conclusion was that white light is a mixture of rays with different refrangibility. Violet bends more than red in ordinary glass, so the prism separates the components by sending them along different paths.
A common mix-up is confusing dispersion with a rainbow’s source. Raindrops also separate sunlight into colors, but they do so through refraction, internal reflection, and dispersion in water droplets.