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William Herschel

How it all started....

William Herschel was the first person to describe the relationship and similarity between heat and light. In three publications in the 'Philosophical Transactions of the Royal Society' (March 27, April 24 and Mai 15, 1800) he writes how he discovered the existence of infrared in the electromagnetic spectrum.
Main element in his research is the use of a prism to break the light in all its colors, and a thermometer to measure the heat that is transferred in these various spectra of light. In his publication on Mai 15, he writes his final conclusion:

"It now being evident that there was a refraction of rays coming from the sun, which though not fit for vision, were yet highly invested with a power of occasioning heat, I proceeded to examine its extend as follows."


Although Herschel is now being considered as the person who discovered infrared, his theories met quite some resistance in the established scientific community. Ten years after Herschels publications, in 1810, no one less than Johann Wolfgang von Goethe ignores his discoveries, by stating in his 'Farbenlehre' about Herschels theories:

"Da es hier nur um Andeutung, nicht aber um Ableitung und Erklaerung dieser Phaenomene zu tun ist, so bemerken wir nur im Vorbeigehen, dass sich am Spektrum unter dem Roten keineswegs das Licht volkommen abschneidet, sondern dass immer noch ein gebrochenes, von seinem Weg abgelenktes, sich hinter dem prismatischen Farbenbild gleichsam herschleichendes Licht zu bemerken ist, so dass man bei naeherer Betrachtung wohl kaum noetig haben wird, zu unsichbaren Strahlen und deren Brechung seine Zuflucht zu nehmen."


["Since there is only a statement, and no deduction and explanation of these phenomena, we note that the spectrum below red is not cut off, but that there is a amount of refracted, disturbed, after the prismatic color range forthgoing evenly distributed light, so that with closer examination there is no need to resort to invisible rays and their refraction."]


After that, Goethe goes on mentioning certain effects of blue and violett rays, but ignores the ultraviolett, although this aspect of light had at that time already been discovered by Johann Wilhelm Ritter, a close friend of Goethe. Ten years before, in 1800, when Herschel discoveres the existence of infrared, Herschel also tried to proof the existence of ultraviolet rays. However, with his prism/thermometer research, he can not proof this existence, so Herschel writes:

" Durch diese letzten Experimente bin ich zufriedenstellend ueberzeugt worden dass keine Strahlen, die ausserhalb des Violetts fallen koentten, irgendeine nachweisbare Kraft haben koennen, weder in Form von Beleuchtung, noch von Aufheizung, und dass diese beiden Kraefte sich fortsetzen durch das prismatische Spektrum und dort enden, wo dass aeusserste Violett verschwindet"


["By these last experiments I am sufficiently convinced that no rays, which could exist outside the violet, can have any provable force, neither in the form of light, nor of heat, and that these two forces prolong along the prismatic spectrum, and ends there where the farthest violets dissapears"]




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