596 THE NERVOUS SYSTEM. 



In Fig. 368 the space between A and B seems to be greater 

 than that between B and c, and yet they are exactly the same. 

 Any space like that between A and B which is subdivided seems 

 larger than that which is undivided, as that between B and c. 

 In Fig. 368 D appears to be higher than it is broad, and E broader 

 than it is high. 



So, too, Zollner's lines (Fig. 369) are very illusory. The hori- 

 zontal lines appear to be far from parallel, and yet if they are 

 looked at from their ends, by turning the page sidewise, their 



/ / / 7 /////// 



\ \ \ \ \ \ v v v v v 



\ \ \ \ \ \ \ \ \ \ \ 



FIG. 369. Zollner's lines. 



parallelism is at once apparent. This is explained by the fact 

 that acute angles are apt to be overestimated and obtuse angles 

 underestimated. 



In Fig. 370 the straight line A appears shorter than the straight 

 line B, though it is of exactly the same length. 



Similar illusions might be multiplied almost indefinitely, and 

 yet with all its imperfections the human eye is a wonderful organ. 

 Some one has said that it is so defective from an optical standpoint 

 that, had he ordered such a piece of apparatus from an optician 



FIG. 370. Illusion of space-perception (Bowditch). 



and it had been delivered with as many defects, he would have 

 returned it and refused to pay for it. It has also been said, in 

 speaking of the crystalline lens, that an optician could make a 

 better lens than Nature has furnished ; but it has also been said 

 that he could not make so good an eye. And finally, Dr. Bow- 

 ditch, in his excellent discussion of "Vision," in the American 

 Text-book of Physiology, well says : " When we reflect upon the 

 difficulty of the problem which Nature has solved, of constructing 

 an optical instrument out of living and growing animal tissue, we 

 cannot fail to be struck by the perfection of the dioptric apparatus 



