What Everyone Believed Before Newton
Before Newton, the prevailing theory was that white light was pure and simple, and that colors were produced by mixing light with darkness — a view held since Aristotle. A prism was thought to "color" light by dirtying it. The red end was thought to result from minimal contamination; the violet end from maximum.
The Crucial Experiment
Newton passed a beam of sunlight through a prism, producing a familiar rainbow spectrum on the wall. But then he did something no one had tried: he isolated a single color from the spectrum — say, red — and passed it through a second prism. The second prism did not produce further colors. Red went in, red came out. This proved that colors were not being added to white light by the prism. The prism was separating colors that were already günümüz.
The Reconstitution
Newton then used a second prism in reverse to recombine the spectrum back into white light. This double proof — decomposition and recomposition — demonstrated that white light is a mixture of all colors, each bent by a different amount when passing through glass (different refractive indices).
The Theory of Color Vision
Newton proposed that different colors correspond to different types of corpuscles (his particle theory of light). Though the corpuscle theory was later superseded by wave and then quantum theories, his conclusion about white light containing all colors was correct. He also introduced the idea of primary colors in his color wheel — though the specific primaries he chose (red, orange, yellow, green, blue, indigo, violet) were partly influenced by his desire to match the seven notes of the musical scale.
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What did Newton discover with a prism?
Newton proved that white light is a mixture of all colors, not a pure substance. When passed through a prism, different colors bend at different angles (different refractive indices), separating the spectrum. A second prism in reverse can recombine them into white light.
Why is Newton's prism experiment important?
It overturned 2,000 years of Aristotelian theory that colors were produced by contaminating white light. It proved that color is a property of light itself, established the foundation of optics, and demonstrated the power of controlled, decisive experimentation.
Why did Newton choose 7 colors in the rainbow?
Newton originally identified 5 colors, then added orange and indigo to make 7 — partly to match the 7 notes of the musical scale, reflecting his belief in a unified natural harmony. The choice of exactly 7 was somewhat arbitrary; the spectrum is continuous with no natural divisions.