VOL. LXXXIir.] PHILOSOPHICAL TRANSACTIONS. 321 



penniformi-radiated muscles. The anterior tendons of all the coats are situated 

 in the same planes, and the posterior ones in the continuations of these planes 

 beyond the axis. Such an arrangement of fibres can be accounted for on no 

 other supposition than that of muscularity. This mass is inclosed in a strong 

 membranous capsule, to which it is loosely connected by minute vessels and 

 nerves; and the connection is more observable near its greatest circumference. 

 Between the mass and its capsule is found a considerable quantity of an aqueous 

 fluid, the liquid of the crystalline. 



I conceive therefore, that when the will is exerted to view an object at a small 

 distance, the influence of the mind is conveyed through the lenticular ganglion, 

 formed from branches of the 3d and 5th pairs of nerves, by the filaments per- 

 forating the sclerotica, to the orbiculus ciliaris, which may be considered as an 

 annular plexus of nerves and vessels; and thence by the ciliary processes to the 

 muscle of the crystalline, which, by the contraction of its fibres, becomes more 

 convex, and collects the diverging rays to a focus on the retina. The disposition 

 of fibres in each coat is admirably adapted to produce this change; for, since the 

 least surface that can contain a given bulk, is that of a sphere (Simpson's 

 Fluxions, p. 486,) the contraction of any surface must bring its contents nearer 

 to a spherical form. The liquid of the crystalline seems to serve as a synovia in 

 facilitating the motion, and to admit a sufficient change of the muscular part, 

 with a smaller motion of the capsule. 



It remains to be inquired, whether these fibres can produce an alteration in the 

 form of the lens sufliciently great to account for the known effects. In the ox's 

 eye, the diameter of the crystalline is 700000ths of an inch, the axis of its an- 

 terior segment 225, of its posterior 350. In the atmosphere it collects parallel 

 rays at the distance of 235000ths. From these data we find, by means of Smith's 

 Optics, art. 366, and a quadratic, that its ratio of refraction is as 10000 to 6074. 

 Hauksbee makes it only as 10000 to 6832.7, but we cannot depend on his ex- 

 periment, since he says that the image of the candle which he viewed was en- 

 larged and distorted; a circumstance that he does not explain, but which was 

 evidently occasioned by the greater density of the central parts. Supposing, 

 with Hauksbee and others, the refraction of the aqueous and vitreous humours 

 equal to that of water, viz. as 10000 to 7465, the ratio of refraction of the 

 crystalline in the eye will be as 10000 to 88O6, and it would collect parallel rays 

 at the distance of 1226 thousandths of an inch; but the distance of the retina 

 from the crystalline is 550 thousandths, and that of the anterior surface of the 

 cornea 250; hence (by Smith, art. 367) the focal distance of the cornea and 

 aqueous humour alone must be 232g. Now supposing the crystalline to assume 

 a spherical form, its diameter will be 642 thousandths, and its focal distance in 

 the eye 926. Then, disregarding the thickness of the cornea, we find (by Smith, 



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