phenomenon differently, the whole landscape becomes differently adjusted. From these experiments we find that this phenomenon is by no means an ordinary sensation, but that it differs from all other sensations in this, that it is the sense itself appearing in the form of a sensation. These experiments prove that it is the sense itself, and nothing else, which reveals itself to us in the particular phenomenon, the eye. If experience informed us that the particular adjustment of some other visual phenomenon (a book, for instance) were essential to our apprehension of all the other phenomena, we should, in the same way, be compelled to regard this book as our sense of sight manifested in one of its own sensations. The book would be to us what the eye now is; it would be our bodily organ: and no a priori reason can be shown why this might not have been the case. All that we can say is, that such is not the finding of experience. Experience points out the eye, and the eye alone, as the visual sensation essential to our apprehension of all our other sensations of vision, and we come at last to regard this sensation as the sense itself. Inveterate association leads us to regard the eye not merely as the organ, but actually as the sense of vision. We find from experience how much depends upon its possession, and we lay claim to it as a part of ourselves with an emphasis that will not be gainsaid.
An interesting enough subject of speculation would be, an inquiry into the gradual steps by which each
