Science
Newton's two-prism trick proved sunlight hides every color
In 1666 Newton let a sunbeam through a hole in his shutter and a prism, spreading it into a rainbow. Passing a single colored ray through a second prism left it unchanged, while recombining the full spectrum restored plain white light. This 'experimentum crucis' proved color is a built-in property of light itself, not something added by glass.