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Published online by Cambridge University Press: 17 January 2013
It is unnecessary to detail to this Society the various ingenious hypotheses which have been proposed to account physiologically for the accommodation of the eye to distinct vision at different distances. In later years, these different theories have been so circumstantially and correctly recapitulated in systematic works (as for instance in Young's Lectures and in Müller's Physiology), that it would be a waste of time to copy and recite them here. I will only do so, then, so far as may be necessary to justify the attempt I have now to make, and to strengthen my views by those of others, as far as they bear upon them.
page 2 note * Quoted by Müller.
page 2 note † Nat. Phil. ii. 589.
page 2 note ‡ Müller's Physiology, translated, p. 1143, 1144.
page 3 note * Brewster in Art. Optics, Encyc. Brit. 7th Edit. p. 513.
page 3 note † See Müller and Brewster.
page 3 note ‡ The forms of curvature of the crystalline lens are said to have been actually ascertained by M. Chossat to be ellipsoidal. It is a curious proof of the vagueness with which this subject has been treated, that, in the clear and able work of Professor Lloyd on Light and Vision, in one page, the form of the surfaces is insisted on as the means of producing distinct vision; and on another, the gradation of density from the centre to the side of the lens; whereas, it is certain, that if the compensation for spherical aberration due to the last cause be correct, the ellipsoidal form will be erroneous. Thus, as in many other cases, the argument for design has been made to prove too much. See Lloyd on Light and Vision, pp. 264-266, who refers to Chossat's paper, Ann. de Chemie, vol. x.
page 4 note * It may be added, that the bullock's eye is perhaps one of the least favourable on which the experiment could be made. Owing to its very great convexity and thickness, it may be presumed that the action of compression above described will be much less visible than in a comparatively flat lens, such as that of man.
page 5 note * I am aware that this is opposed to the experiment of Mr Ramsden and Sir E. Home, which seems to shew a protrusion of the eyeball. Supposing it correct, that protrusion must be equally the result of muscular action producing pressure, due perhaps to the oblique muscles antagonising the recti; for it is difficult to see where else it can be sought.
page 5 note † “In all animals the crystalline lens grows firmer with age.” Brewster Edin. Encyc., Art. Optics, p. 475.
page 5 note ‡ In the Annales de Chimie, vol. x., published in 1819.
page 6 note * M. Chossat's experiments were made on the lens of an ox; but Dr Allen Thomson tells me that, without knowing his results, he had arrived at a similar conclusion, as to the opposite kind of curvature in the cornea and in the lens of the human eye; the surface of the former lying without, and the latter within the surface of the osculating sphere.