Where this discovery comes from
White light is made of colours
In 1666 Isaac Newton let a thin beam of sunlight through a hole in his window shutter and onto a glass prism. It spread into a long band of colours on the far wall, not a round spot.
One thing to hold: A glass prism, a sunny window, and a sheet of white card.
Why it matters: Newton then let only one colour through a slit and onto a second prism. It bent again but did not change colour. He called it his crucial experiment: the colours are in the white light, and the glass only sorts them.
What we don’t know: Newton described it in a letter to the Royal Society in 1672; the date 1666 comes from his own later account. Other people’s first attempts to repeat it did not always work, because their prisms were poorer.
Dates:
- 1666 Newton’s prism at the window shutter.
- 1672 His letter to the Royal Society.
- 1704 Opticks is published.