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What did William Herschel discover about infrared radiation in 1800?
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William Herschel
Sir William Herschel, detail of an oil painting by L. Abbott, 1785; in the National Portrait Gallery, London.
In 1800, the German-born British astronomer Sir William Herschel discovered infrared radiation while conducting experiments with sunlight.12
By using a prism to disperse sunlight into its constituent colors, Herschel explored the spectrum with a thermometer. He observed that the temperature increased beyond the red end of the visible light range, identifying a form of invisible radiation that could be detected as a sensation of warmth. This discovery revealed a portion of the electromagnetic spectrum that exists at frequencies lower than visible red light.23