_Argument from the Affection of a Portion of the Retina._--The fact that in vision a certain portion of the retina in length and breadth is actually affected by the light falling on it, has been supposed by some to be conclusive of the fact that we perceive the length and breadth of the external object by the eye. This does not necessarily follow. As Dr. Brown contends, it is equally true that a certain part of the organ of smell is affected by odors, and a certain part of the auditory nerve is affected by sounds, yet we are not conscious of any perception of extension by either of these organs; we neither smell nor hear the length, and breadth, and magnitude of objects; nor is there any reason to suppose that the particular portion of the retina affected has any thing to do with the original sensation of sight. _Amount of the preceding Arguments._--These arguments however, do not strike me as conclusive. They merely show the _possibility_ that extension and figure _may be_ acquired rather than original perceptions. They do not amount to positive evidence that they _are_ so. _An Argument to the Contrary._--On the other hand, there is one consideration of a positive character, which to most minds will be likely to outweigh the merely negative arguments already adduced. Color is a property of light, and light comes to us reflected from objects occupying space; we perceive it only as we perceive it spread over and reflected from some surface. Extension, then, surface expansion of the reflecting object, is the indispensable condition of the visibility of light itself, and so of color, as reflected from the object. Now it is difficult to persuade ourselves that what we know to be an essential condition of the perception of color, and what we seem to perceive along with the color, and cannot, even in thought, wholly separate from it, is not, after all, really perceived by the eye.