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On: the'Hale-seon eroumtill Bodie. 31 
they appear in their true place, though not always of their true 
size, for this depends on the diameter of the pin-hole. There is 
however another very important circumstance which contributes 
to the erect position of external objects—the axis of the pin-hole 
and our eye are strictly parallel, and all the rays which pass 
through the centre of this axis carry an erect impression of the 
object whence they emanate. 
43. I observed above that when the pin-hole is near the eye, 
its lenticular property is apparent. If we hold a pin between the 
eye and the pin-hole, the pin will be inverted. The reason of 
this is obvious, for according to the 23d section, the halo is len- 
ticular in the direction of its parallelism with the edge or surface 
of the body on which it rests. If the pin-hole were oblong, or 
if the aperture were a long slit instead of a round hole, the sha- 
dow of any slender object before the eye would remain the same 
as to position, but be reversed as to movements. But the pin- 
hole being a perfect lens—for it is completely filled by the halo— 
any shadow cast on its surface will be reversed both in position 
and movement. ‘The character of these halos never varies; they 
act upon one another in a sensible manner and always produce 
the same results.  s> 
44. Should a doubt remain as to the lenticularity of this halo 
on the pin-hole, we have only to observe the figure which ap- 
pears on its surface. On looking steadily at the pin-hole we shall 
perceive that the rays of light from a candle, and which are 
brought to a focus on the lens of our own eye, give to the cere- 
bral organs of vision an exact representation of all specks, flaws, 
spots, and movements of fluids which actually exist within the 
eyeball. I say cerebral organs, because a true knowledge of vis- 
ion must convince us that the figure which appears to be in the 
pin-hole cannot by any possibility be painted or impressed ¢here, 
and if not there, certainly not on any part of the interior of the 
eyeball. The very circumstance of being able to see any part 
of the interior of our own eye should settle the question of the 
seat of vision, and prove that the eyeball and its internal appara- 
tus are merely for the purpose of transmitting rays of light and 
not images; that the images which are the result of these rays, 
are impressed on the cerebral organs with the first touch of light 
on the elastic machinery of the eye, and never come to a focus 
_ on the retina or on any other part of the interior of the eyeball. 
_ But I have pursued this branch of the subject elsewhere. 
coed 
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