20 
APPLICATION OF THE ARGUMENT. 
produce, not by a simple action or effect, but by a combi¬ 
nation of actions and effects, the result which is ultimately 
wanted. And forasmuch as this organ would have to ope¬ 
rate under different circumstances, with strong degrees of 
light and with weak degrees, upon near objects, and upon 
remote ones, and these differences demanded, according to 
the laws by which the transmission of light is regulated, a 
corresponding diversity of structure ; that the aperture, 
for example, through which the light passes, should be 
larger or less; the lenses rounder or flatter, or that their 
distance from the tablet, upon which the picture is delinea¬ 
ted, should be shortened or lengthened: this, I say, being 
the case, and the difficulty to which the eye was to be 
adapted, we find its several parts capable of being occa¬ 
sionally changed, and a most artificial apparatus provided 
to produce that change. This is far beyond the common 
regulator of a watch, which requires the touch of a foreign 
hand to set it; but it is not altogether unlike Harrison’s con¬ 
trivance for making a watch regulate itself, by inserting 
within it a machinery, which, by the artful use of the dif¬ 
ferent expansion of metals, preserves the equability of the 
motion under all the various temperatures of heat and cold 
in which the instrument may happen to be placed. The 
ingenuity of this last contrivance has been justly praised. 
Shall, therefore, a structure which differs from it, chiefly by 
surpassing it, be accounted no contrivance at all ? or, if it 
be a contrivance, that it is without a contriver? 
But this, though much, is not the whole : by different 
species of animals the faculty we are describing is possess¬ 
ed, in degrees suited to the different range of vision which 
their mode of life, and of procuring their food, requires. 
Birds, for instance, in general, procure their food by means 
of their beak; and, the distance between the eye and the 
point of the beak being small, it becomes necessary that 
they should have the power of seeing very near objects 
distinctly. On the other hand, from being often elevated 
much above the ground, living in air, and moving through 
it with great velocity, they require, for their safety, as well 
as for assisting them in descrying their prey, a power 
of seeing at a great distance; a power, of which, in birds 
of rapine, surprising examples are given. The fact ac¬ 
cordingly is, that two peculiarities are found in the eyes 
of birds, both tending to facilitate the change upon which 
the adjustment of the eye to different distances depends. 
The one is a bony, yet, in most species, a flexible rim or 
