sensations, and could give him no aid in solving his problem. We cannot go further into this matter at present.[6] The mere flash of light which follows the touch upon the optic nerve represents itself as something _without_; nor was colour, we imagine, ever felt, but under some _form_ more or less distinct; although in the human being the eye seems to depend on the touch far more than in other animals, for its further instruction. [6] It is seldom any action of a limb is performed without the concurrence of several muscles; and, if the action is at all energetic, a number of muscles are brought into play as an equipoise or balance; the infant, therefore, would be sadly puzzled amongst its muscular sensations, supposing that it had them. Besides, it seems clear that those movements we see an infant make with its arms and legs are, in the first instance, as little _voluntary_ as the muscular movements it makes for the purpose of respiration. There is an animal life within us, dependent on its own laws of irritability. Over a portion of this the developed thought or reason gains dominion; over a large portion the will never has any hold; over another portion, as in the organs of respiration, it has an intermittent and divided empire. We learn voluntary movement by doing that instinctively and spontaneously which we afterwards do from forethought. We have moved our arm; we wish to do the like again, (and to our wonder, if we then had intelligence enough to wonder,) we do it. But although the eye is cognisant of form as well as colour, it is in the sensation of colour that we must seek the primitive pleasure derived from this organ. And probably the first reason why form pleases is this, that the boundaries of form are also the lines of contrast of colour. It is a general law of all sensation that, if it be continued, our susceptibility to it declines. It was necessary that the eye should be always open. Its susceptibility is sustained by the perpetual contrast of colours. Whether the contrast is sudden, or whether one hue shades gradually into another, we see here an original and primary source of pleasure. A constant variety, in some way produced, is essential to the maintenance of the pleasure derived from colour.