His name is especially associated with two main branches of investigation - aeronautics, and the exploration of the infra-red portions of the solar spectrum.
Been made use of by Becquerel in his investigations of infra-red radiations.
Calor, heat), a term invented by John Tyndall to describe an optical phenomenon, the essential feature of which is the conversion of rays belonging to the dark infra-red portion of the spectrum into the more refrangible visible rays, i.e.
Festing, who examined the infra-red absorption of a number of substances.
The infra-red requires special appliances; it has been examined visually by the help of phosphorescent plates (Becquerel), and with special photographic plates (Abney); but the most efficient way is to use the bolometer or radiomicrometer; by this means some 500 or 600 lines have been mapped.
It would apply only if the spectrum had no infra-red and ultraviolet extensions.
Both rock-salt and carbon bisulphide are extremely transparent to the luminous and also to the infra-red rays The iodine in the solution, however, has the property of absorbing the luminous rays, while transmitting the infra-red rays copiously, so that in sufficient thicknesses the solution appears nearly black.
If suitable values are chosen for these constants, the formula can be made to represent the dispersion of ordinary transparent media within the visible spectrum very well, but when extended to the infra-red region it often departs considerably from the truth, and it fails altogether in cases of anomalous dispersion.
It should be mentioned that the infra-red rays have a remarkable damping effect on the phenomena of phosphorescence, a fact which has.
Paschen 6 has further extended the method and added a number of infra-red lines to the spectra of helium, argon, oxygen and other elements.