here than anywhere else. So we must appreciate that we see with the cones right in the middle of the field of view, but as we go to the periphery we have the other cells, the rods, Now the interesting thing is that in the retina each of the cells which is sensitive to light is not connected by a fiber directly to the optic nerve, but is connected to many other cells, which are themselves connected to each other There are several kinds of cells: there are cells that carry the information toward the optic nerve, but there are others that are mainly interconnected"horizontally There are essentially four kinds of cells, but we shall not go into these details now The main thing we emphasize is that the light signal is already being"thought about. "That is to say, the information from the various cells does not immediately go to the brain, spot for spot, but in the retina a certain amount of the informatio s already been digested, by a combining of the information from several visual receptors. It is important to understand that some brain-function phenomena occur in the eye itself. One of the most striking phenomena of vision is the dark adaptation of eye. If we go into the dark from a brightly lighted room, we cannot see very we ell for a while, but gradually things become more and more apparent, and eventually we can see something where we could see nothing before. If the intensity of the light is very low, the things that we see have no color. It is known that this dark adapted vision is amost entirely due to the rods, while the vision in bright light is ult, there are a number of phe that we can easily appreciate because of this transfer of function from the cones and rods together There are many situations in which, if the light intensity were stronger, we could see color, and we would find these things quite beautiful. One example is that through a telescope we nearly always see"black and white""images of faint nebulae, but w. C. Miller of the Mt. wilson and Palomar Observatories had the patience to make color pictures of some of these objects. Nobody has ever really seen these colors with the eye, but they are not artificial colors, it is merely that the light intensity is not strong enough for the cones in our eye to see them. Among the more spectacular such objects are the ring nebula and the Crab nebula.The former shows a beautiful blue inner part, with a bright red outer halo, and the latter shows a general bluish haze permeated by bright red-orange filaments In the bright light, apparently, the rods are at very low sensitivity but, in the dark, as time goes on they pick up their ability to see light. The variations in light intensity for which one can adapt is over a million to one. Nature does not do all this with just one kind of cell, but she passes her job from bright-light-seeing ells, the color-seeing Among the interesting consequences of this shift is, first, that there is no color, and econd, that there is a difference in the relative brightness of differently colored objects. It turns out that the rods see better toward the blue than the cones do and the cones can see, for example, deep red light, while the rods find that absolutely impossible to see. So red light is black so far as the rods are concerned. Thus two pieces of colored paper, say blue and red, in which the red might be even brighter than the blue in good light, will, in the dark, appear completely reversed. It is a very striking effect. If we are in the dark and can find a magazine or something that has colors and, befo know for sure what the colo dge the lighter and darker areas, and if we then carry the magazine into the light, we may see this ble shift between which was the brightest color and which was not The phenomenon is called the Purkinje effect. dashed curve represents the sensitivity of dark i.e., using the rods, while the solid curve represents it in the light. We see that the k sensitivity of the rods is in the green region and that of the cones is more in the yellow region. If there is a red-colored page(red is about 650 mu)we can see it if it is brightly lighted, but in the dark it is almost invisible