The ideas of _different degrees_ of this resistance are gained by repeated experience, and when age furnishes the ability to understand language, the names of hardness, softness, roughness, and the like, are given to these ideas. In the use of his muscles, also, the infant must first acquire its ideas of _extension_ and _figure_; for it must be where resistance to muscular effort ceases that he must feel that the cause ceases to exist. The little being extends his hand--an object intervenes which interrupts his muscular motions; he grasps this object, and wherever this feeling of resistance exists, there he feels that the cause of it exists, and that after he has passed certain limits it does not exist. _Figure_ is defined as the _limits of extension_, and, of course, it can be seen that ideas of figure can only be gained by thus finding the limits of extension. It has formerly been supposed that ideas of _extension_ and _figure_ were gained by the eye, but later experiments and discussions show that the sense of feeling, including muscular motion, is the medium by which these ideas are first gained, and that afterward the eye, by the principle of association, acquires the power of distinguishing figure and distance. There is much enjoyment resulting from the sense of touch in many ways, a large portion of which is almost unnoticed. Much also included under the term _comfort_ results from this sense. Much of that which is agreeable in clothing and in objects around us is of this nature. Besides this, there are many endearments of friendship and affection that gain expression only through this medium. _Vision._ The organ of vision is the eye, which is one of the most curious and wonderful parts of the human frame, and displays in astonishing variety the wisdom and skill of its Designer. The eye consists of a round ball, formed externally of various coverings, and within of humors of different degrees of consistency. The front part of the eye, which is exposed to view, has a small opening in it, which admits the rays of light within this ball, while it is by the operation of light on the nerves, which are spread in fine net-work over the interior, that _sight_ is produced. In examining the mechanism of the eye, a great variety of contrivances appear, all aiding in accomplishing the object of vision. In the first place, we may observe its modes of protection and defense. The lid is a soft, moist wiper, which, with a motion quick as lightning, protects the eye from outward violence, cleanses it from dust, veils it from overpowering radiance, and in hours of repose entirely excludes the light. On its edge is the fringing lash, which intercepts floating matter that might otherwise intrude, while above is spread the eyebrow, which, like a thatch, obstructs the drops that heat or toil accumulate on the brow.