There is a certain pre-arrangement here of the circumstances to suit the convenience of explanation. The little arm of the infant being very closely fastened to its own little body, it could hardly move it fifty or a thousand times in succession, or even once, without its muscular sensation terminating in the sense of resistance, or pressure, which is but another form of the sense of touch. In short, this would be always sooner or later the consequent upon this muscular sensation. And it appears very evident that "the little reasoner," more especially if he held the same doctrine as Brown on the nature of cause and effect, would look no further than the _first_ sensation for the cause of the _second_. There would be few instances in his limited experience more marked of invariable antecedence and consequence than this,--that the muscular sensation would sooner or later be followed by a tactual one. If we could suppose it possible, that the infant logician had to make the discovery of an external world by an effort of reasoning upon its sensations, we should say that this case was the least likely of any to lead him to the discovery--the least likely to impel him to look out of the circle of sensations for a cause of them. Mere sensation of any kind, reason on it how we will, cannot account for the perception of external objects, which is another and separate fact. We are reduced to admit that it is by a simple primary law of our constitution that the organs of sense (which may with equal propriety be called the organs of perception) convey to us a knowledge of the external world. We touch, and a tangible extended body is made known to us; we open our eyes, and a visible body is before us. Dr Brown, adopting and refining upon Berkeley's theory of vision, attributes originally nothing more than the mere sensation of colour to the eye, which sensation, by association with that of touch, becomes extended, so to speak, over an external surface, and defined into limited figures. We are not disposed to lay any greater stress than Dr Brown himself upon the _image_ said to be traced upon the retina; but we say that the eye, as well as the touch, immediately informs us of external surface and definite figure. There is, it is true, a _sensation_ of colour apart from the _perception_. This may be separated, in our reflection, from all external surface. It is a _pleasure_ which colour gives, and which enters largely into the complex sentiments of beauty. But our notion of colour itself we cannot dissociate from external surface: we cannot think of colour but as something outward. And if it comes to us originally under the condition of external surface, it must also present itself originally under certain forms and figures; for only where the whole field of vision is occupied by one unvaried colour, as when the eye is fixed upon a cloudless sky, could there be the perception of surface without some figure, more or less defined on it.