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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    their weakness or inconstancy. Consideration of the difficulty of focalizing rays of wide differences of refrangibility must also not be forgotten. Were the extremes not shut out, chromatic aberration would certainly be more of a disturbance than at present; and, that the “difficulty” is real is also shown e. g., by the fact of presbyopia. The inelasticity of the lens is complete before old age is reached. First, as to the ultra-violet, the insignificance of the total energy of these rays is perceived by noticing the tiny curve and extent of activity of these undula- tions figured in the little triangle beyond H. of Fig. II. Not only is the energy too inconsiderable to produce sufficient organic reaction of the ocular mechanism, as compared with the adjacent red space, but the varying quantities of such rays, resulting from the ever-changing remnants left over after the absorptions of the atmosphere have been satisfied, renders constancy of stim- ulus impossible, and the eye naturally fails to develop response to stimuli, or excludes them from the retina, because they are so weak and capricious. We must, moreover, not fail to recollect the exaggerated importance and mistaken supposition of extent of the rays of this part of the spectrum, naturally engendered by their influence in photography. A line must be drawn some- where by nature, and the remarkable fact seems to be that the violet rays should not have been excluded from color-production. The limitation of the chromatic scale should not be a cause of critical complaint, but its extension is rather a source of delighted wonder. In considering The Infra-Red Rays, so rich in the total amount of energy and so magnificent in the extent of their wave-lengths, it would at first blush appear that the preceding considerations could have no force or application; but this is a mistake. We think exactly the same reasons suffi- cient to account for their non-participation in vision. Observe first, that though three-fifths of the total energy of the spectrum, is in this region, it is spread over a space six times as great. Now it is apparent that amplitude of range beyond a certain nec- essary and satisfactory amount, would be of no advantage. How