754 POPULAR SCIENCE MONTHLY. 



to the eye. Objects beyond our reach, as the stars or the clouds, 

 are not truthfully pictured. Accuracy of perception grows less 

 as distance increases. The unfamiliar lends itself readily to illu- 

 sions ; the familiar is recognized chiefly by breaks in continuity. 

 The real forces of Nature are hidden by their grandeur, by their 

 immortality. Men see the form of the surface, 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 unusual 

 conditions. It occurs 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 hyperaesthesia of the 

 sense of smell. Hypersesthesia of any of the senses would be to 

 most animals a source of confusion and danger rather than of 

 safety. 



Man's high development of the brain in large degree takes the 

 place of acuteness of special senses. It is part of the function of 

 the will to keep down the senses ; and in his perception of exter- 

 nal relations he is aided by the devices of science, which may be 

 taken up or laid down at will. By means of instruments of pre- 

 cision any of the senses may be aided to an enormous degree, and 

 at the same time the personal equation or individual source of 

 error is largely eliminated. The use of instruments of precision 

 is the special characteristic of the advance of science. No instru- 

 ment of precision can give us the ultimate essence of any part of 

 the universe. No scientific experiment can do away with the 

 measure of human experience as the basis of intelligibility. At 

 the same time we can throw large illumination into " the dimly 

 lighted room " in which, according to Balfour, the phenomena of 

 consciousness take place. By the simple process of photography, 

 for example, we may reproduce the objects of our environment. 

 That such pictures do express phases of reality admits of no 

 doubt, for in the photographic camera all personal equation is 

 eliminated. As to form of outline and reflection of light, the 

 " sun paints true," and the paintings thus made by means of the 

 action of nonliving matter produce on our senses impressions co- 

 inciding with those of the outside world itself. 



How do we know this is true ? Because belief in it adds to 

 the safety of life. We can trust our lives to it. If it were an 

 illusion it would kill, because action based on illusion leads to 

 death. 



One can trust his life, for example, to the message sent on a 

 telegraph wire. All who travel by rail do this daily. One can 

 trust his life to the reading of a thermometer. The chemist's 



