Herschels experiment. In 1800, Sir Frederick Herschel (1738-1822) discovered infrared light while trying to find if there was a difference in temperature between the different colours in a spectrum. He used three thermometers, one to measure a single colour while the other two were outside the spectrum as controls. When he placed a thermometer beyond visible red light the highest temperature was measured. He called them calorific rays. This discovery also lead to the discovery of ultraviolet but by Johann Wilhelm Ritter. While the textbook version of the experiment will work, Herschels method will probably produce better results. The thermometer bulbs are painted black to improve the readings.