366 THE SENSORIAL FUNCTIONS. 



visible world only two, namely, length and breadth. The 

 objects of sight constitute a kind of language, which Nature 

 addresses to our eyes, and by wliich she conveys informa- 

 tion most important to our welfare. As, in any language, 

 the words or sounds bear no resemblance to the things 

 they denote, so in this particular language the visible ob- 

 jects bear no sort of resemblance to the tangible objects they 



represent. 



The theory of Berkeley received complete confirmation by 

 the circumstances attending the well known case, described 

 by Cheselden, of a boy, who, from being blind from birth, 

 suddenly acquired, at the age of twelve, the power of see- 

 ing, by the removal of a cataract. He at first imagined that 

 all the objects he saw touched his eyes, as what he felt did 

 his skin; and he was unable either to estimate distances 

 by the sight alone, or even to distinguish one object from 

 another, until he had compared the visual with what has been 

 called the tact ualim-pression. 



This theory also affords a satisfactory solution of a ques- 

 tion which has frequently been supposed to involve consi- 

 derable difficulty; namely, how it happens that we see ob- 

 jects in their true situation, when their images on the retina, 

 by which we see them, are inverted. To expect that the 

 impression from an inverted image on the retina should pro- 

 duce the perception of a similar position in the object viewed, 

 is to commit the error of mistaking these images for the real 

 objects of perception, whereas they are only the means which 

 suggest the true perceptions. It is not the eye which sees; 

 it is the mind. The analogy which the optical part of the 

 €ye bears to a camera obscura has perhaps contributed to the 

 fallacy in question; for, in using that instrument, we really 

 contemplate the image which is received on the paper, and re- 

 flected from it to our eyes. But in our own vision nothing 

 of this kind takes place. Far from there being any contem- 

 plation by the mind of the image on the retina, we are ut- 

 terly unconscious that such an image exists, and still less 

 can we be sensible of the position of the image with respect 



