It is clear, then, that _the lights and colours of the landscape depend on many things beside the stimuli there presented_; they depend on contrast, on the previous adaptation of the eye, on the presence or absence of after-images. The main reason that we do not notice all these influences is that we ordinarily view the landscape, not for itself, but for what it means; it shows us the familiar trees and stream and houses, and we take their stability for granted. That is the main reason; it is not the only one. We have said, for instance, that the normal retina is totally colour-blind along its outer edge, and partially colour-blind for some distance in toward the centre; _the edge of the landscape ought therefore to be colourless_, and a certain outlying portion of it ought to appear simply as blue and yellow. There is no hint of these differences; and the explanation is that we are accustomed to turn our eyes directly towards what we want to see, and therefore to view it with all three of the daylight films; head and eyes =move= so easily, and we see so much better with the centre of the retina, that we totally disregard the altered look of things seen ‘out of the corner of the eye.’ Even if we do not, we are likely to _remember_ how the things appear in direct vision; we paint them over, so to speak, with =memory-colours=, colours that represent their natural or average appearance at the centre of the visual field; indeed, we may _paint these colours over the whole landscape, and in that way correct the changes due to contrast or adaptation_. We always talk of a certain book as brown; we recognise it in all lights, and in all states of the eye, by its brown colour; we _see_ it, in memory-colour, as brown; whereas, if that same brown were shown us in all the different circumstances without our knowing it to be the same, it might give us sensations of yellow, of pale brown, of deep brown, of black. These two factors, _movement of the eyes and memory-colour_, lead us to overlook, in great part, the actual variation of lights and colours in the landscape. A final word may be added regarding _the likeness of sight and smell_. Odours and colours fade out by adaptation; odours, like lights and colours, contrast, and even cancel one another; and smell-stimuli as well as sight-stimuli mix to produce new and simple sensations. It is highly probable that the sensory cells of smell are the seat of only a few chemical processes, by whose combination all the wealth of odours is created, just as the cone-cells of the retina are the seat of those three reversible processes (black-white, blue-yellow, red-green) whose combination endows us with the variety of daylight vision. We have as yet, however, no such definite grounds for hypothesis as we have in the case of sight; we cannot even guess what these processes are, or how many of them are taking place in the smell-membrane.