through the vitreous humour, less dense, and which preserves, without 

 increasing it, the refraction produced by the crystalline lens. The rays, 

 gathered into one, strike on a single point of the retina, and produce the 

 impression which gives us the idea of certain properties of the body 

 which reflect them. As the retina embraces the vitreous humour, it pre- 

 sents a very extensive surface to the contact of the rays, which enables us 

 to behold, at once, a great diversity of objects, variously situated towards 

 us, even when we or these objects change our relative situation*. The 

 luminous rays, refracted by the transparent parts of the eye, form there- 

 fore, in the interior of the organ, a cone, of which the base covers the 

 cornea, and applies to that of the external luminous cone, whilst its apex 

 is on some point of the retina. It is conceived, generally, that the lumi- 

 nous cones issuing from all points of the object beheld, cross in their 

 passage through the eye, so that the object is imaged on the retina re- 

 versed Admitting this opinion, established on a physical experiment, 

 we have to inquire, why we see objects upright, whilst their image is re- 

 versed on the retina. The best explanation we possess of this phenome- 

 na, we owe to the philosopher Berkeley, who proposed it in his English 

 work, entitled Theory of Vision, Sec. In his opinion, there is no need of 

 the touch to correct this error into which sight ought to betray us. As 

 we refer all our sensations to ourselves, the uprightness of the object is 

 only relative, and its inversion really exists at the bottom of the eye. 



radiated fibres, giving rise to certain states of pupil, is relative to the extent, to which 

 the irritation proceeds along 1 the axis of the nerves and vessels, and affects either set of 

 fibres. 



According to this view of the Subject, compression of the brain, or an insensible state 

 of the optic nerve, is followed by expansion of the pupil, because the first impression 

 requisite to contraction of the orbicular fibres, cannot be made, unless occasionally to a 



pupil. The pup) 



with worms, conformably to what is gciun-iilly observed in the animal economy, namely, 

 that all orbicular muscles, when no adjoining 1 irritation exists, exhibit a greater or less 

 degree of relaxation as the vital energies are more or less diminished. It would appear, 

 in a debilitated state of the system, that the nervous influence proceeding from the len- 

 ticular ganglion, is insufficient to the 'purpose of exciting fully the orbicular fibres of 

 the iris, and, at the same time, the retina perhaps, possesses that low degree of sensi- 

 bility to the irritation of light which is followed by an adequate effect upon the nerves 

 supplying the iris. Indeed, it seems, under the circumstances just referred to, where 

 irritation is generally present in the abdominal viscera, that nervous influence is secreted 

 in the brain and parts adjoining in an insufficient manner, and consequently the dimi- 

 nished activity of the cerebral and ganglial nerves supplying the various structures of 

 the eye is the result. When, however, irritation exists in the brain, or when an increase 

 of the circulation occurs in that organ, without overwhelming- its powers, accompanied 

 with, or preceded by, debility, the pupil contracts, or even remains contracted, because, 

 in consequence of such irritation or increase of circulation in the brain and connected 

 parts, the sensibility and nervous activity are heightened. 



* The rays of light may be said to penetrate or traverse the demi-transparent tissue 

 of the retina, and, as it were, to search through the nervous pulp, when they arrive at 

 the choroid coat, which is designed, in a great measure, to absorb these rays. Does any 

 intimate combination take place between the nervous pulp and the light, which may 

 give rise to that sensation which follows" a violent compression of the globe of the eye 

 in an obscure situation? The spots which are observable after having had the eye 

 fixed for a considerable time, on certain coloured objects, do they arise from this sort 

 of impregnation of the retina, or rather of a portion of it, with the rays of lighter, as is 

 more generally believed, has the sensibility of the retina become partially increased Or 

 diminished by the circumstance of inaction, or of exercise Copland- 



