I f the image o f an object, formed after refraftion, is greater or
lefs than the angle formed at the eye, by the rays proceeding
from the extremities o f the object itfelf, the objeft will appear
alfo proportionably enlarged or diminilhed ; fo that i f the eye
approaches to, or removes from, the laft image, the object will
appear to increafe or diminifh, tliough the eye Ihould in reality
remove from it in one cafe, or approach towards it in the other;
becaufe the image takes place o f the objeft, and is confidered
inftead of it.
The apparent diftance o f an objeft from the eye, is not meafured
by the real diftance from the laft image; for, as the apparent
diftance is eftimated principally by the ideas we have o f their fize, it
follows, that when we fee objects, whole images are tncieafed o r
diminilhed by refraftion, we naturally judge them to be nearer
or further from the eye, in proportion to the fize thereof, when
compared to that with which we are acquainted. The apparent
diftance o f an objeft is confiderably affefted by the brightnefs,
diftinctnels, and magnitude thereof. Now as thefe circumftances
are, in a certain degree, altered by the refraftion of the rays, m
their paffing through different mediums, they will alfo, in fome
meafure, affeft the eftimation of the apparent diftance.
In the theory o f vifion, it is neceffary to be cautious not to
confound the organs o f vifion with the being that perceives, or
with the perceptive faculty. The eye is not that which fees, it
is only the organ by which we lee. A man cannot fee the fatel-
lites o f Jupiter but by a telefcope. Does he conclude from this,
that it is the telefcope that fees thofe ftars P By no means; fiich a
conclufion would be abfurd. It is no lefs abfurd to conclude,
g that
that it is the eye that fees. The telefcope is an artificial organ
o f fight, but it fees not. The eye is a natural organ o f fight, by
which we fee; but the natural organ fees as little as the artificial.
The eye is a machine, molt admirably contrived for refrafting
the rays of light, and forming a diftinft pifture o f objefts upon
the retina; but it fees neither the objeft nor the pifture. It can
form the pifture after it is taken out of the head, but no vifion
enfues. Even when it is in it’s proper place, and perfeftly found,
it is well known, that an obftruftion in the optic nerve takes
away vifion, though the eye has performed all that belongs to it.*
For ufelefs was this textur’d f wonder made,
Were nature, beauteous objeft ! undifplayed;
Thofe both in vain, the objeft and the fight,
Wrapt from the radiance o f revealing light;
As vain the bright illuminating beam,
Unwafted by the medium’s airy ftream:
Yet vain the textur’d eye, and objeft fair,
The funny luftre, and continuous a ir;
Annull’d and blank this grand illuftrious feene,
All, all it’s grace and lifelefs glories vain;
Till fromth’ E t e r n a l fprung this effluent foul,
Form’d to infpeft, and comprehend the whole.];
F 2 .
* Reia on the Intellectual Powers of Man, p. 78,
t The eye.
+ Brooke’s Univerfal Beauty, p. 88.