This motion has its two aspects. There are two aspects because we have developed two principal faculties: sight and hearing. One aspect appeals to our hearing, the other to our sight. The aspect of movement or vibration which appeals to our hearing is what we call audible and what we term sound. The aspect which appeals to our sight we call light, we call it color, and we call it visible. In point of fact, all that is visible, all that is audible - what is it in its origin? It is motion, it is movement, it is vibration, it is one and the same thing. Therefore, even in that which is audible, in that which is called sound, those who can see trace color, and to those who can hear, even the sound of the color is audible.