SENSE OF VISION. 883 



increase of facility which he derived from it. 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 dis- 

 tinguish them by the latter sense. This question was answered by Locke in 

 the negative; and, as appears from the facts just stated, with justice. 



884. The actions performed by many new-born animals do not constitute any 

 valid objection to this view ; for all that is indicated by them is, that certain 

 sensations give rise to movements adapted to supply the wants to which they 

 relate. Such instinctive actions are, as already pointed out, much more nume- 

 rous in the lower Animals than in the higher, and in the young of the Human 

 species than in the adult ( 792) ; and they do not afford any proof that definite 

 notions, such as we acquire, of the forms and properties 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. 



885. 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 in- 

 verted. 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, direc- 

 tion," which has been supported by Sir D. Brewster, and other eminent Philo- 

 sophers. This law aflirms, 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 object 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, however, 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 determined by Volkmann, that 

 the lines of direction cross each other in a point a little behind the crystalline 

 lens j and that they must thus fall at such different angles on different points of 

 the retina, that no general law can be laid down respecting them. Moreover, 

 even supposing that such a law were a correct statement of the general fact, it 

 would not afford any real 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 always bear that in mind, 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; the latter being the result of the operation 

 of the Sensory impression on the Cerebrum, but having a nature as distinct as 

 that of any other effect can be from that of its cause. Further, it has been shown 

 that there is in Man a complete absence of any relation but such as experi- 

 ence develops, between the perceptions derived through the Sight, and those ac- 

 quired from the Touch. Hence there is no more difficulty in understanding, that 

 an inverted picture upon the retina should convey to us a notion of the external 

 world, which harmonizes with that acquired through the sense of touch, than 

 there is in comprehending the existence of any of those intuitive perceptions of 

 animals, which are so much more removed from the teachings of our own ex- 

 perience ( 792). It is justly remarked by Miiller that, "if we do see objects 

 inverted [or rather, if the picture on the retina be inverted], the only proof we 

 can possibly have of it is that afforded by the study of the laws of Optics ; and, if 



