The case of association which we are now considering, brings to view another circumstance, of some importance in tracing the effects of this great law of our nature. It is this: that in any associated cluster, the idea of sight is almost always the prevalent part. The visible idea is that which takes the lead, as it were; and serves as the suggesting principle to the rest. So it happens in the combination of the sensations of colour, with those of extension and figure: the visible idea stands foremost; and calls up the rest. It calls them up also with such intensity, that both the remarkable cases of association are exemplified. Whenever we have the sensation of colour, we cannot avoid having the ideas of distance, of extension, and figure, along with it; nor can we avoid having them in such intimate union with the ocular sensation, that they appear to be that sensation itself. {347} This is the whole of what is ever supposed to be in the case. Of no phenomenon of the human mind is the developement more complete or more important. Our belief that we see the shape, and size, and distance of the object we look at, is as perfect as belief in any instance can be. But this belief is nothing more than a case of very close association. The case of belief by association, any one may illustrate further, for himself, by recollecting some of the commonest cases of optical deception. If we look at a landscape with the naked eye, we believe the several objects before us, the men, the animals, the trees, the houses, the hills, to be at certain distances. If we next look at them through a telescope, they seem as if they were brought near; we have the distinct belief of their proximity, and though a belief immediately corrected by accompanying reflection, it is not only belief, but a belief that we can by no means shake off. We can, after this, invert the telescope, and then we cannot help believing, that the nearest objects are removed to a distance. Now what is it that the telescope performs in these two instances? It modifies in a certain manner the rays of light to the eye. The rays, proceeding from the objects, are so distributed on the eye, as they would be if the distance of the objects was less, or greater. Instantly we have the belief that it is less or greater; because, the sensation of the eye, by means of the glass, is made to resemble that which it receives, when objects are seen at a smaller or greater distance; and each of the sensations calls up that idea of distance which is habitually associated with it.