SENSE OF VISION. 415 



sociate the two sets of ideas ; and then, setting her down, said, " So, puss, I 

 shall know you another time." A similar instance has come under the Au- 

 thor's own knowledge ; but the subject of it was scarcely old enough to pre- 

 sent phenomena so striking. One curious circumstance was remarked of him, 

 which fully confirms (if confirmation were wanting) the view here given. 

 For some time after the sight was tolerably clear, the lad preferred finding his 

 way through his father's house, to which he had been quite accustomed when 

 blind, by touch rather than by sight, the use of the latter sense appearing to 

 perplex rather than to assist him ; but, when learning a new locality, he em- 

 ployed his sight, and evidently perceived the increase of facility which he de- 

 rived from it. 



542. The question has been proposed, whether a person born blind, who 

 was able by the sense of Touch to distinguish a cube from a sphere, would, 

 on suddenly obtaining his Sight, be able to distinguish them by the latter 

 sense. This question was answered by Locke in the negative ; and probably 

 with justice. It is no real objection to such a reply, that a new-born animal 

 seeks the nipple of its mother, when informed of its proximity by sight ; for 

 all that is indicated by this fact is, that the sensation excites an intuitive feel- 

 ing of desire, which gives rise to movements adapted to gratify it. Such in- 

 stinctive actions, founded upon intuitive perceptions, are, as already pointed 

 out, much more numerous in the lower Animals than in the higher, and in the 

 young of the Human species than in the adult ( 428) ; and they do not afford 

 any proof that definite notions, such as we acquire, of the forms and proper- 

 ties of external objects, are possessed by the animals which exhibit them. 

 We shall now examine, a little more in detail, into the means by which we 

 gain such notions, and the data on which they are founded. 



543. The first point to be determined, is one which has been a fruitful 

 source of discussion, the cause of erect vision, the picture upon the retina 

 being inverted. Many solutions of it have been attempted; but they are for the 

 most part rather specious than really satisfactory. That which has been of late 

 years the most in vogue, is founded upon what was styled the Law of Visible 

 Direction, which has been supported by Sir D. Brewster, and other eminent 

 Philosophers. This law affirms, that every object is seen in the direction of 

 the perpendicular to that point of the retina, on which its image is formed ; 

 or, in other words, that, as all the perpendiculars to the several points of the 

 inner surface of a sphere meet in the centre, the line of direction of any ob- 

 ject is identical with the prolonged radius of the sphere, drawn from the point 

 at which its image is made upon the retina. Upon close examination, how- 

 ever, it is found that this law cannot be optically correct ; since the lines of 

 direction cross each other at a point much anterior to the centre of the globe ; 

 as may be determined by drawing a diagram upon a large scale, and laying 

 down the course of the rays received by the eye, according to the curvatures 

 and refractive powers of its different parts. In this manner it has been deter- 

 mined by Volkmann, that the lines of direction cross each other in a point a 

 little behind the crystalline lens ; and that they will thus fall at such differ- 

 ent angles on different points of the retina, that no general law can be laid 

 down respecting them. It may be questioned, moreover, whether such a law 

 would afford any assistance in explaining the phenomenon ; since, after all, 

 it is requisite to assume an intuitive application of it, in supposing the mind 

 to derive its ideas of the relative situations of objects, from the imagined line 

 of direction. A much simpler and more direct explanation may be given. 

 We must remember that, which we have had occasion to notice in regard to all 

 the other senses, the broad line of distinction between the sensation and the 

 perception or elementary notion; and this is still more clearly shown by the 

 complete absence of any relation, but such as experience developes, between 



