The Eye, in fact, not only fulfils the action of focussing rays of light--like an Opera Glass or a Telescope--but it might be compared to another instrument, a Photographic Camera, in respect of the fact that it forms a picture of the outer world which it throws on a sensitive plate at the back--the Retina. But then, again, it is unlike any of these "machines," in the fact that it was never made by any Optician, human or divine, for any one definite purpose. On the contrary, as we know, it has grown, it has evolved; it has come down to us over the centuries, and over thousands and thousands of centuries, from dim beginnings in the lowliest organisms who first conceived the faculty of Sight, continually modified, continually shapen by small increments in various directions, in accordance with the myriad needs of a myriad creatures, living, some of them in water, some of them in air, requiring some of them to see at close quarters, some at great distances, some by one kind of light, some by another, and so forth. So that to-day it not only contains a great range of inherited, yet latent, faculties, but it is actually, in its complex structure, an epitome and partial record of its own extraordinary history. As an instance of this last point, let me remind you that Sight was originally a differentiation of Touch. The light, the shadows, falling on the sensitive general surface of a primitive organism provoke a tactile irritation. In the course of evolution this sense specialises itself at some point of the surface into what we call Sight. Now, to-day, when the little picture formed by the fore-part of the Human Eye falls upon the Retina at the back, it falls upon a screen formed by the myriad congregated finger-tips, so to speak, of the optic nerve--the rods and cones, so-called--which cover like a mosaic the whole ground of the Retina, and _feel_ with their sensitive points the images of the objects in the outer world. And so Sight is still Touch--it is the power of feeling or touching at a distance--as one sometimes in fact becomes aware in looking at things.