390 AIM AND PROGRESS OF PHYSICAL SCIENCE. 



examination of the actual facts at once destroys in the 

 most merciless manner all belief in a preordained harmony 

 of the inner and external world. 



I need not call to mind the startling and unexpected re- 

 sults of ophthalmometrical and optical research which have 

 proved the eye to be a by no means more perfect optical 

 instrument than those constructed by human hands ; but, 

 on the contrary, to exhibit, in addition to the faults 

 inseparable from any dioptric instrument, others that in 

 an artificial instrument we should severely condemn ; nor 

 need I remind you that the ear conveys to us sounds from 

 without in no wise in the ratio of their actual intensity, 

 but strangely resolves them and modifies them, intensify- 

 ing or weakening them in very different degrees, ac- 

 cording to their varieties of pitch. 



These anomalies, however, are as nothing compared 

 with those to be met with in examining the nature of the 

 sensations by which we become acquainted with the 

 various properties of the objects surrounding us. Here 

 it can at once be proved that no kind and no degree of 

 similarity exists between the quality of a sensation and 

 the quality of the agent inducing it, and portrayed by it. 



In its leading features this was demonstrated by Johannes 

 Miiller in his law of the Specific Action of the Senses. Ac- 

 cording to him, each nerve of sense possesses a peculiar kind 

 of sensation. A nerve, we know, can be rendered active 

 by a vast number of exciting agents, and the same agent 

 may likewise affect different organs of sense ; but however 

 it be brought about, we never have in nerves of sight 

 any other sensation than that of light ; in the nerves of 

 the ear any other than a sensation of sound; in short, 

 in each individual nerve of sense only that sensation 

 which corresponds to its peculiar specific action. The 

 most marked differences in the qualities of sensation, 

 in other words, those between the sensations of different 



