Festing, who examined the infra-red absorption of a number of substances.
It will be seen that the maximum ordinates lie upon the curve A9 = constant dotted in the figure, and so, as the temperature of the ideal body rises, the wave-length of most intense radiation shifts from the infra-red X towards the luminous part of the spectrum.
3 Although the vibrations in the infra-red have a considerably greater intensity, they are more difficult to register than those in the ultra-violet.
Been made use of by Becquerel in his investigations of infra-red radiations.
He especially devoted himself to investigations of the radiation of heat from the sun and its absorption by the earth's atmosphere, and to that end devised various delicate methods and instruments, including his electric compensation pyrheliometer, invented in 1893, and apparatus for obtaining a photographic representation of the infra-red spectrum (1895).