XVII. Now let us consider for an instant what would be the effect of continually repeating an expression of a beautiful thought to any other of the senses at times when the mind could not address that sense to the understanding of it. Suppose that in time of serious occupation, of stern business, a companion should repeat in our ears continually some favorite passage of poetry, over and over again all day long. We should not only soon be utterly sick and weary of the sound of it, but that sound would at the end of the day have so sunk into the habit of the ear that the entire meaning of the passage would be dead to us, and it would ever thenceforward require some effort to fix and recover it. The music of it would not meanwhile have aided the business in hand, while its own delightfulness would thenceforward be in a measure destroyed. It is the same with every other form of definite thought. If you violently present its expression to the senses, at times when the mind is otherwise engaged, that expression will be ineffective at the time, and will have its sharpness and clearness destroyed forever. Much more if you present it to the mind at times when it is painfully affected or disturbed, or if you associate the expression of pleasant thought with incongruous circumstances, you will affect that expression thenceforward with a painful color for ever. XVIII. Apply this to expressions of thought received by the eye. Remember that the eye is at your mercy more than the ear. "The eye it cannot choose but see." Its nerve is not so easily numbed as that of the ear, and it is often busied in tracing and watching forms when the ear is at rest. Now if you present lovely forms to it when it cannot call the mind to help it in its work, and among objects of vulgar use and unhappy position, you will neither please the eye nor elevate the vulgar object. But you will fill and weary the eye with the beautiful form, and you will infect that form itself with the vulgarity of the thing to which you have violently attached it. It will never be of much use to you any more; you have killed or defiled it; its freshness and purity are gone. You will have to pass it through the fire of much thought before you will cleanse it, and warm it with much love before it will revive.