174 Mr. Young's Observations on Vision . 
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 third and fifth pairs of nerves, by the fila- 
ments perforating 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 ad- 
mirably 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. 4,86) 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 faci- 
litating 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 pro- 
duce an alteration in the form of the lens sufficiently great to 
account for the known effects. 
In the ox's eye, the diameter of the crystalline is 700 thou- 
sandths of an inch, the axis of its anterior segment 225, of 
its posterior 350. In the atmosphere it collects parallel rays 
at the distance of 235 thousandths. 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 6574. FIauksbee 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 enlarged and distorted; a circumstance that he 
does not explain, but which was evidently occasioned by the 
