Analysis of information sources in references of the Wikipedia article "Electromagnetic spectrum" in English language version.
He directed sunlight through a glass prism to create a spectrum [...] and then measured the temperature of each colour. [...] He found that the temperatures of the colours increased from the violet to the red part of the spectrum. [...] Herschel decided to measure the temperature just beyond the red of the spectrum in a region where no sunlight was visible. To his surprise, he found that this region had the highest temperature of all.
{{cite book}}: ISBN / Date incompatibility (help)Ritter [...] hypothesized that there must also be invisible radiation beyond the violet end of the spectrum and commenced experiments to confirm his speculation. He began working with silver chloride, a substance decomposed by light, measuring the speed at which different colours of light broke it down. [...] Ritter [...] demonstrated that the fastest rate of decomposition occurred with radiation that could not be seen, but that existed in a region beyond the violet. Ritter initially referred to the new type of radiation as chemical rays, but the title of ultraviolet radiation eventually became the preferred term.
He directed sunlight through a glass prism to create a spectrum [...] and then measured the temperature of each colour. [...] He found that the temperatures of the colours increased from the violet to the red part of the spectrum. [...] Herschel decided to measure the temperature just beyond the red of the spectrum in a region where no sunlight was visible. To his surprise, he found that this region had the highest temperature of all.