360 FOOT-NOTES TO EVOLUTION. 



trustworthy when it can not result in action. Objects 

 too small to be touched are invisible to the eye. Objects 

 beyond our reach, as the stars or the clouds, are not 

 truthfully pictured. Accuracy of percep- 

 Sensation truth- tion grow s less as the square of the dis- 

 ful in the degree Unce increases It is a rec ognised law 

 that action is 



possible psychology that only medium varia- 



tions and differences are correctly esti- 

 mated. The senses deal correctly only with the near, 

 the mind only with the common. The unfamiliar lends 

 itself readily to illusions. The familiar is recognised 

 chiefly by breaks in continuity. The real forces of 

 Nature are hidden by their grandeur, by their duration. 

 Men see the waves on the surface of the sea, but not the 

 mighty tides that move beneath it. Again, the senses 

 are less acute than the mechanism of sense organs would 

 make possible. This is shown through occasional cases 

 of hyperaesthesia or ultra-sensitiveness. This occurs in 

 abnormal individuals or in diseased conditions. It oc- 

 curs normally in creatures whose lives in some sense 

 depend on it. Thus some of the most remarkable exhibi- 

 tions of "mind reading" may be paralleled by retriever 

 dogs, whose reason for existence is found in the hyper- 

 aesthesia of the sense of smell. Hyperaesthesia of more 

 than one of the senses would be to most animals a 

 source of confusion and danger rather than of safety. 

 The high development of the brain in man in large de- 

 gree takes the place of acuteness of special senses. It 

 is part of the function of the will to regulate the senses 

 and to suppress those impressions which should not lead 

 to action. 



In his perception of external relations man is aided 

 by the devices of science, which may be taken up or laid 

 down at will. By means of instruments of precision any 

 of the senses may be extended to an enormous degree, 



