the case of longitudinal distance in vision, we perceive _colour_ at one distance rather than at another. Yet there is as little reason, from the nature of the organic changes themselves, to suppose, that different affections of our auditory nerves should _originally_ give us different notions of distance, as that such notions should originally be produced by different affections of the retina: and, as in sight and hearing, so it is far from improbable, that, in all our senses, there may, by the reciprocal influence of these upon each other, or by the repeated lessons of individual experience in each, be a similar modification of the original simple feelings, which, in that first stage of existence that opened to us the world and its phenomena, each individual organ separately afforded. Our reasoning with respect to them, therefore, as original organs of sense, may, perhaps, be as false, as our chemical reasoning would be, were we to attempt to infer the properties of an uncombined acid, or alkali, from our observation of the very different properties of a neutral salt, into the composition of which we know that the acid or the alkali has entered. If, indeed, it were in our power to be introduced to a society, like that of which Diderot speaks, in his Letter on the Deaf and Dumb, and to hold communication with them, all our doubts on this subject would be removed. “What a strange society,” says he, “would five persons make, each of them endowed with one only of our five different senses; and no two of the party with the same sense! There can be no doubt, that, differing, as they must differ, in all their views of nature, they would treat each other as madmen, and that each would look upon the others with all due contempt. It is, indeed, only an image of what is happening every moment in the world; we have but one sense, and we judge of every thing.”[63]--“There is, however,” he justly remarks, “_one_ science, though but one science, in which the whole society of the different senses might agree,--the science which has relation to the _properties of number_. They might each arrive, by their separate abstractions, at the sublimest speculations of arithmetic and algebra; they might fathom the depths of analysis, and propose and resolve problems of the most complicated equations, as if they were all so many Diophantuses. It is perhaps,” he adds, “what the oyster is doing in its shell.”[64]