Retinal insensibility to ultra-violet and infra-red rays / by L. Webster Fox and Geo. M. Gould.

  • Fox, Lawrance Webster, 1853-1931.
Date:
1886
Catalogue details

Licence: Public Domain Mark

Credit: Retinal insensibility to ultra-violet and infra-red rays / by L. Webster Fox and Geo. M. Gould. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    The Normal Solar Spectrum is here extended so that we have in about 12 inches a graphic delineation of what was before crushed into one-twelfth the space for purposes of comparison. In this way we get a com- parative view of relative values of the visible and invisible spec- tra. At this point it may be well to throw in a word of ex- planation as to the unit of measurement used, or of the proper meaning to be attached to the broken curve; it represents the abstract kinetic value or absolute energy contained in the radia- tions apart from all considerations of the receiving substance. Much of the confusion existing concerning these questions ari- ses from many misleading or positively absurd diagrams in old text-books or articles devoted to the “ plebification” of knowl- edge concerning these matters. It is now agreed that the kine- tic value of all ether waves is measurable in terms of heat, and that the greatest energy of the spectrum is in yellow; at high noon ' it is about wave-length 0.55 //, whilst about sunset it is near wave-length 0.65 owing to the increased absorption of the shorter waves by the greater thickness of the at- mospheric layer. The difference of effect produced by an imping- ing series of ether-waves arises solely from the merely accidental nature of the receiving medium. The energy of the ultra-violet rays is so small as to be almost infinitesimal, but because these rays happen to correspond in beat to the vibrational frequency of the molecules of the haloid salts of silver,and the highly impor- portant consequences resulting therefrom in the art of photog- raphy, their importance in an absolute or in a visual sense has been greatly overestimated. It is a startling fact that a photo- graph can be taken by the aid of these vibrations in a room ab- solutely black and without light to a normal eye. It has been a popular fashion tocall these rays actinic, and the infra-red, “heat” waves; those be-tween, “light” waves. But every ray whatsoever is a heat ray, and the rays producing the greatest heat are pre- cisely those producing, when falling upon the retina, the greatest visual effect. The energy-cure, the heat-curve,and the light-curve are in great part identical, and the apex of this curve is about wave-length O.SSjgi^t as shown in the diagram. Thus a nomen-