THE BACK WALL OF THE EYE.
It is a remarkable fact that every object we see has its picture formed upon the back wall of our eyes. The eye is a darkened chamber, and the whole of the front part of it acts as a lens to bring the rays of light coming from objects we wish to see to a focus on its back wall, thus forming a picture there as distinct as the picture formed in the camera obscura of the photographer. This has not only been proved by the laws of optics, but has been actually demonstrated in the eyes of rabbits and other animals. Experimenters have held an object before the eye of a rabbit for a few moments, and have then killed the animal and removed the eye as quickly as possible, and laid its back wall bare, and have distinctly seen there the picture of the object upon which the eye had been fixed. It is a truly wonderful fact that these pictures upon the back wall of the eye can be changed so rapidly that the picture of the object last looked at disappears in an instant and makes way for the picture of the next. We know that the picture formed on the back wall of the eye is carried back to the brain by the optic nerve, but there our knowledge stops. Science cannot tell us how the brain, and through it the mind, completes the act of seeing. It is there that the finite and the infinite touch, and, as our minds are finite, we cannot comprehend the infinite.
But there is enough that we can understand, and it shall be my endeavor in this paper to make some plain statements that will help as a guide in the preservation of those wonderful and useful organs.