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.

    9/22 (page 7)
    ing our globe produce a general absorption, rendering the whole spectrum less bright and less hot; with infinite degrees this man- ner of absorption passes into what may more specifically be called molecular, producing the dark telluric lines of the spectrum The number of these lines increases rapidly from noon till at sunset the spectrum is crowded with them. In ascending a mountain many of the telluric lines fade out even from the spectrum of high-noon at sea-level. We get nearly as much light from the sky on an average as from the sun direct, and the total value of this absorbent power of the atmosphere is concluded by Prof.Langley to be as high as 40 per cent., double the estimate of all previous investigators. If, then, we could, with our eye as at present constructed, rise above ouiyitmosphere, the sun would appear distinctly blueish, because the maximum energy-point of the spectrum would at this elevation be in the (at present) green part of the spectrum, our white light being a compound of only a part of the visible solar-rays, many of the longer ones having been quenched by the atmosphere acting like ever-present red- dish semi-transparent spectacles. Fig. Ill gives a representation of the energy or heat curves of the visible spectrum, 1, outside our atmosphere; 2, within the same at noon, and 3, just before sunset. The apex of the curve is seen to be farther toward A. with each increase of atmospheric depth. Beyond our atmosphere it is at about wave-length 0.50 //., whilst at noon and evening at sea-level, it is, as we have seen, at about 0.55 and 0.65^respec- tively. It should be borne in mind that though the light rays suffer a far larger relative absorption than the infra-red, the apex of the curve nevertheless remains comparatively unfissured and is always elevated far above any of the peaks of the infra-red rays. The Exclusion from Visual Participation of the Ultra- Violet and Infra-Red Rays seems natural from a glance at either of these diagrams, but es- pecially so from the first and second. In a sentence, it is be- cause the eye has learned to react to the strongest and most con- stant stimulus or classes of stimuli, and has learned to extin- guish or exclude those vibrations that would only confuse by