On sight, and its relation to inverted images / by Wm. Munro.

  • Munro, William.
Date:
[1858]
Catalogue details

Licence: Public Domain Mark

Credit: On sight, and its relation to inverted images / by Wm. Munro. 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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    attempted to prove in the following manner,—after talcing the eye of an ox, and leaving the vitreous humour perfect.they took a piece of white paper or other transparent material and witli it covered the posterior part of tlie eye, thus placing it in the position of the retina, when on opposing the convex surface of the cornea to some outward olyect, the image of the same appeared on the coating hehind, but inverted. Having seen this, they came to the conclusion that such would require to he the case with the human eye, and the impression it loft on the brain, and strange to say, every one had powerful argu- ments to support his own opinion. Amongst the leaders of this theory were some of the most cele- brated men of tlieir day, and as ever happens, many took it as a received truth ; allowing their mental powers to lie dormant and desisting from any research though at the same time, the minute physiological and cliemical structures of the organ were well known. By taking either a double convex or piano convex lens and placing before it an object, it will, after passing through sivAx a medium fall towards the perpendicular, and if allowed to proceed far enough after passing through the lens, the rays will again diverge, but this time the ujipcr ones of the original hgure will be downwards and the lower ones iipwards, and according as the distance is nearer or further removed from the lens after forming this image, its appearance will be smaller or greater. ISuch actually does take ]ilaco witliin'the tlie eye of man and domestic animals, and the experiment on the bullock's eye is essen- tially correct after giving allowance for the change of shape of the organ, and immobility of the iris— Yet, though the artificial retina will receive an impression, it is far from being a true one of the complete process wliicli reaches the brain, and this as will be seen accounts for the errors which happened. The best anatomists of the day are agreed that the retina con- sists of three parts, viz. : an outer membrane called Jacobs, which consists of little piles stuck at right angles into the retina and though the use of those cannot be actually arrived at, they seem to act somewhat as a discharging battery, when vision is required to be more intent, by pressing more firmly upon the anterior and more inner parts by the blood-vessels of the choroid been more fully injected. Yet they dont seem to be more immediately concerned in vision., but to be loosely connected with the parts which lie next them, and are'actuallj'^ those most concerned in the jjrocess. These con- sist of an external and an internal layer of nerve cells, with an intermediate layer of fibres, still between these and the viti-€)U3 humour, lies a delicate net work of arteries and veins, held together by cellular membrane, through which vision must pass before it reaches the brain. On this delicate curtain the inverted image is depicted, but it is to be remembered that in the state of health the eye can be both fitted for distance and exclude nearly all, but the number of rays required foi- perfect vision, so that the size, brightness, and distance of an object, are properties which require some instruction before being appreciated. The rays which arc actually required for vision, fall