PROGRESS OF PSYCHOLOGY. 453 



sets our notions of the specific functions of nerve- 

 centres." 



There is reason to suspect that Miiller's law, while 

 expressing an important truth, has inclined many 

 physiologists to put in a full stop prematurely. Let 

 us notice how Loeb regards it; his revolutionary or 

 evolutionary outlook is always stimulating. 



" Whether a blow, an electric current, or ether-vibra- 

 tions of about 0.0008-0.0004 millimetres wave length 

 stimulate the retina, the sensation is always a specific 

 one, namely, light, while a blow or an electric current 

 produces sensations of sound in the ear. This so- 

 called law of the specific energy of the sense-organs is 

 not peculiar to the sense-organs; it applies, as was 

 emphasised by Sachs, to all living matter ; it even holds 

 good for machines. It is in reality only another ex- 

 pression for the fact that the eye, the ear, and every 

 living organ are able to convert energy in but one 

 definite form that is, that they are special machines. 

 The determination of the way in which this transforma- 

 tion of energy occurs in the various organs would be 

 the explanation of the specific energy of the various 

 senses." 



" Physiology gives us no answer to the latter ques- 

 tion. The idea of specific energy has always been re- 

 garded as the terminus for the investigation of the 

 sense-organs. All the more credit is due Mach and 

 Hering for first having advanced beyond that limit 

 with their chemical theory of colour sensations. 

 Mach has recently expressed the opinion that chemical 

 conditions lie at the foundation of sensations in gen- 

 eral." * 



E. H. Weber (1795-18T8). Weber was one of 

 those who introduced precise physical methods into 

 physiological investigation. He belongs to the 



* Comparative Physiology of the Brain and Comparative 

 Psychology, 1901, pp. 290-291. 



