14 
APPLICATION OF THE ARGUMENT. 
refracted by a mol*e convex surface than when it passes 
out of air into the eye. Accordingly we find, that the eye 
of a fish, in that part of it called the crystalline lens, is much 
rounder than the eye of terrestrial animals. [Plate II. fig. 1.] 
What plainer manifestation of design can there be than this 
difference ? What could a mathematical instrument-maker 
have done more, to show his knowledge of his principle, 
his application of that knowledge, his suiting of his means 
to his end; 1 will not say to display the compass or excel¬ 
lence of his skill and art, for in these all comparison is 
indecorous, but to testify counsel, choice, consideration, 
purpose ? 
To some it may appear a difference sufficient to destroy 
all similitude between the eye and the telescope, that the 
one is a perceiving organ, the other an unperceiving instru¬ 
ment. The fact is, that they are both instruments. And, 
as to the mechanism, at least as to mechanism being em¬ 
ployed, and even as to the kind of it, this circumstance va¬ 
ries not the analogy at all. For, observe what the consti¬ 
tution of the eye is. [Plate II. fig. 2.] It is necessary, in 
order to produce distinct vision, that an image or picture of 
the object be formed at the bottom of the eye. Whence this 
necessity arises, or how the picture is connected with the 
sensation, or contributes to it, it may be difficult, nay we 
will confess, if you please, impossible for us to search out. 
But the present question is not concerned in the inquiry. It 
may be true, that, in this, and in other instances, we trace 
mechanical contrivance a certain way; and that then we 
come to something which is not mechanical, or which is in¬ 
scrutable. But this affects not the certainty of our inves¬ 
tigation, as far as we have gone. The difference between 
an animal and an automatic statue, consists in this,—that, 
in the animal, we trace the mechanism to a certain point, 
and then we are stopped; either the mechanism becoming 
too subtile for our discernment, or something else beside 
the known laws of mechanism taking place: wdiereas, in 
the automaton, for the comparatively few motions of which 
it is capable, we trace the mechanism throughout. But, 
up to the limit, the reasoning is as clear and certain in the 
one case as in the other. In the example before us, it is a 
matter of certainty, because it is a matter which experience 
and observation demonstrate, that the formation of an im¬ 
age at the bottom of the eye is necessary to perfect vision. 
The image itself can be shown. Whatever affects the dis¬ 
tinctness of the image, affects the distinctness of the vision. 
The formation then of such an image being necessary (no 
