Common Sense Applied to Religion; Or, The Bible and the People

by Catharine Esther Beecher

In examining the mechanism of the eye, a great variety of contrivances appear, all aiding in accomplishing the object of vision. In the first place, we may observe its modes of protection and defense. The lid is a soft, moist wiper, which, with a motion quick as lightning, protects the eye from outward violence, cleanses it from dust, veils it from overpowering radiance, and in hours of repose entirely excludes the light. On its edge is the fringing lash, which intercepts floating matter that might otherwise intrude, while above is spread the eyebrow, which, like a thatch, obstructs the drops that heat or toil accumulate on the brow.

We next observe the organs of motion with which the eye is furnished, and which, with complicated strings and pulleys, can turn it every way at the will of the intelligent agent. The pupil or opening of the eye, also, is so constructed, with its minute and multiplied circular and crossing muscles, that it can contract or expand in size just in proportion as the light varies in intensity.

The ball of the eye is filled with three substances of different degrees of density. One is a watery humor, near the front of the eye; back of this, and suspended by two muscles, is the solid lens of the eye, or the crystalline humor; and the remainder of the eye, in which this lens is imbedded, consists of the vitreous humor, which is of the consistence of jelly. These all have different degrees of transparency, and are so nicely adjusted that the rays of light, which start from every point in all bodies in diverging lines, are by these humors made to converge and meet in points on the retina, or the nerve of the eye, forming there a small picture, exactly of the same proportions, though not the same size, as the scene which is spread before the eye.

When the outer covering of the back part of the eye is removed, the objects which are in front of the eye may be discerned, delicately portrayed in all their perfect colors and proportions, on the retina which lines the interior. It is this impression of light on the optic nerve which gives our ideas of light and colors.

The eye is also formed in such a way that it can alter its shape and become somewhat oblong, while at the same time its lens is projected forward or drawn back. The object of this contrivance is to obtain an equally perfect picture of distant and of near objects.

Our ideas of shape and size at first are not gained by the eye, but by the sense of touch. After considerable experience we learn to determine shape and size by the eye. Experiments made upon persons born blind and restored to sight furnish many curious facts to support this assertion.

When the eye first admits the light, all objects appear to touch the eye, and are all a confused mass of different colors. But by continual observation, and by the aid of the sense of touch, objects gradually are separated from each other, and are then regarded as separate and distinct existences.

The eye is so formed that the picture of any object on the retina varies in size according to its distance. Two objects of equal size will make a different picture on the back of the eye, according to the distance at which they are held. The ideas of size at first are regulated by the proportions of this picture in the eye, until by experience it is found that this is an incorrect mode, and that it is necessary to judge of the distance of a body before we can determine its size. This accounts for the fact that objects appear to us so different according as we conceive of their distance, and that we are often deceived in the size of bodies because we have no mode of determining their distance.

But it appears also that our ideas of distance are gained, not by the eye alone, but by the eye and the sense of feeling united. A child by the sense of feeling learns the size of his cup or his playthings. He sees them removed, and that their apparent size diminishes. They are returned to him, and he finds them unaltered in size. When attempting to recover them, he finds that when they look very small he is obliged to pass over a much greater distance to gain them than when they appear large, and that the distance is always in exact proportion to their apparent size. In this way, by oft-repeated experiments, the infant reasoner learns to judge both of the size and distance of objects. From this it appears that, in determining the size of an object, we previously form some judgment of its distance, and likewise that, in finding the distance, we first determine the size.

The shape of objects is learned altogether by the sense of feeling. It has before been stated that at the first exercise of vision every thing is a confused mass of different colors, and all appearing to touch the eye. By the aid of the hands the separate existence of different bodies is detected, and the feeling of touch, which once was the sole mode of determining shape, is now associated with a certain form or picture on the eye, so that, in process of time, the eye becomes the principal judge of shape.