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Herschel infrared light experiments, artwork. In 1800, the British astronomer William Herschel (1738-1822) carried out a series of experiments that led to his discovery of infrared light. Here, sunlight was split into its colours (spectrum of colours labelled on table) by refraction in a prism (upper left). Thermometers (right) were used to investigate the heating effects of different colours. The hottest area, beyond visible red light, became known as infrared radiation. This illustration (plate XI) accompanied the second of Herschel's four papers on this topic (read 24 April 1800), published in volume 90 of 'Philosophical Transactions' (Royal Society of London).
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