208 PHYSIOLOGY. 



stationary or in motion. Now, suppose a person was look* 

 ing at a church with a tree standing at its side, he would 

 have in each eye an actual inverted panorama of the objects, 

 painted in a more beautiful, correct, and delicate manner 

 than any effort of art can ever hope to exhibit, as follows. 



Fig. 16. 



28. But if the images of objects are inverted, why do we 

 see things erect ? Locke, Buffon, Diderot, and other great 

 philosophers, supposed that infants at first see things upside 

 down, and afterwards learn to correct their erroneous sensa- 

 tion, by comparing the information obtained by touch with 

 that acquired by sight. And not only this, they maintain- 

 ed that infants see every object double, and all at the same 

 distance, until experience corrects their errors. Berkeley, 

 however, contended, that we judge of the position of objects 

 by comparing them with our own ; and as we see ourselves 

 as well as every thing else wrong side up, or inverted, ex- 

 ternal bodies are in the same relation to us as if they were 

 erect. But in that case, the boy who stoops down and looks 

 at objects between his legs, ought certainly to see them 

 wrong side up ; but though a little confused perhaps at first, 

 he soon sees in that way as well as any other. This diffi- 

 culty is easily explained by what is called the law of visible 

 direction ; that is, each point of an object is seen perpendi- 

 cular to the point of the retina on which its image falls. 

 The surface of the retina being concave, and nearly as pos- 



