25 
on the Mechanism of the Eye. 
deserving of comparison. I shall proceed to relate a variety of 
experiments which appear to be the most proper to decide on 
the truth of each of these suppositions, and to examine such 
arguments as have been brought forwards, against the opinion 
which I shall endeavour to maintain; and I shall conclude with 
some anatomical illustrations of the capacity of the organs 
of various classes of animals, for the functions attributed to 
them. 
III. Of all the external senses, the eye is generally supposed 
to be by far the best understood; yet so complicated and so 
diversified are its powers, that many of them have been hitherto 
uninvestigated; and on others, much laborious research has been 
spent in vain. It cannot indeed be denied, that we are capable 
of explaining the use and operation of its different parts, in a 
far more satisfactory and interesting manner than those of the 
ear, which is the only organ that can be strictly compared with 
it; since, in smelling, tasting, and feeling, the objects to be ex- 
amined come almost unprepared into immediate contact with 
the extremities of the nerves; and the only difficulty is, in con- 
ceiving the nature of the effect produced by them, and its com- 
munication to the sensorium. But the eye and the ear are 
merely preparatory organs, calculated for transmitting the im- 
pressions of light and sound to the retina, and to the termina- 
tion of the soft auditory nerve. In the eye, light is conveyed to 
the retina, without any change of the nature of its propagation: 
in the ear, it is very probable, that instead of the successive motion 
of different parts of the same elastic medium, the small bones 
transmit the vibrations of sound, as passive inelastic hard bodies, 
obeying the motions of the air in their whole extent at the same 
instant. In the eye, we judge very precisely of the direction of 
mdccci. E 
