Let us examine the magical effects of music. They are of two orders; the purely auditive, and the intellectual or moral. The first stop at the ear, the second pass to the brain and to the heart; and one may be admirably organized for the former, yet unable to appreciate the latter. Two persons listen to a sonata, both hear the _material_ music, but the intellectual and moral effects are not the same on both. Both perceive the least defect in the time or in the instrument, both admire the art of the composer, both are charmed; but while the heart of one is unmoved, the brain and the heart of the other are bounding with delight, the power of his fancy is multiplied, thoughts and images crowd upon his mind, as though he had caught inspiration from the magic notes of the music. His heart is transported with tenderness, melancholy, hatred, love, anger, generosity, and courage. He is under a magical influence which, moves him in spite of himself; the vibrations of a chord have raised in his heart a mysterious tempest which the might of reason can hardly quiet. 109. From this we must conclude, that besides the ordinary relations between objects and the organs of the senses, there are other relations still more intimate and more delicate between these objects and our organic system, and that these latter are as certain as the former. In them there is greater variety of individuals, and the conditions necessary to produce determinate results are less known, but there can be no doubt of their existence, and this in the eyes of sound philosophy is sufficient to dissipate those absurd suppositions which would pretend to undermine the edifice of our knowledge. 110. Thus, then, the objection is answered, which says: "If we had another sense, what would it tell us?" Nothing which would destroy the certainty of our knowledge, or the nature and order of our ideas. The only new result would be _one more_ added to the many ways in which objects now affect us. The same thing would happen to us as to a man who after being deprived of the sense of smell, should suddenly regain it: he would have one sensation more; the same thing would happen to us as to a man who experiences a new sentiment which he had not known before: he has one affection more. New impressions have their own rank, neither interfering with, nor changing those which previously existed. BOOK THIRD. EXTENSION AND SPACE. CHAPTER I. EXTENSION INSEPARABLE FROM THE IDEA OF BODY. 1. Having seen that among the objects of our sensations, extension alone has any external existence for us as any thing more than a principle of causality, let us now try to understand what extension is.