The material of an object is perceived by the senses. We see that it is blue or green or brown; we may touch it and note that it is rough or smooth, hard or soft, warm or cold. But the expressiveness of the object, its value for the emotions, does not stop with its merely material qualities, but comes with our grasp of the "relations" which it embodies; and these relations, transmitted through material by the senses, are apprehended by the mind. There are, of course, elementary data of sense-perception, such as color and sound. It may be that I prefer red to yellow because my eye is so constituted as to function harmoniously with a rate of vibration represented by 450 billions per second, and discordantly with a rate of vibration represented by 526 billions per second. So also with tones of a given pitch. But though simple color and simple sound have each the power to please the senses, yet in actual experience neither color nor sound is perceived abstractly, apart from its embodiment in form. Color is felt as the property of some concrete object, as the crimson of a rose, the dye of some fabric or garment, the blue of the sky, which, though we know it to be the infinite extension of atmosphere and ether, we nevertheless conceive as a dome, with curvature and the definite boundary of the horizon. Sound in and of itself has pitch and _timbre_, qualities of pure sensation; but even with the perception of sound the element of form enters in, for we hear it with a consciousness of its duration--long or short--or of its relation to other sounds, heard or imagined.