ON THE PSYCHO-PHYSICAL VIEW OF NATURE. 483 



duced as belong to the qualitative or order region of 

 one definite sense, and that every stimulus which can at 

 all affect this nerve fibre produces only sensations be- 

 longing to this definite order." l This means that, for 

 instance, any effective stimulus of the optic nerve 

 apparatus produces only and always the sensation of 

 light, whereas the same stimulus would in the auditory 

 nerve apparatus, if effective, produce the sensation of 

 sound. " The same vibrations of the ether which the 

 eye perceives as light, the nerves of the skin perceive as 

 heat. The same vibrations of air which the latter per- 

 ceive as a tremor, the ear perceives as a musical sound." 2 

 The quality of our sensations does not depend on the 

 stimulus but on the nervous apparatus. 



Helmholtz has said 3 that the law of the specific 

 energies forms the most important advance which the 

 physiology of the senses has made in recent times, and 

 has even compared it with the discovery of the law of 

 gravitation. 4 As we shall see immediately, he has him- 



1 See Helmholtz, ' Handbuch der ] much limited to Germany, and there 



Physiologischen Optik,' 2te Aufl. , \ also almost entirely to what may 



1896, p. 233. j be called Miiller's school, in which 



- Helmholtz, ' Vortriige und Re- i Helmholtz is the central ngure. In 



den,' vol. ii. p. 224 ; also ' Physiolo- j England the doctrine was subjected 



gische Optik,' p. 249 : " Miiller's law to a full criticism by George Henry 



of the specific energies marks an Lewes, an important thinker, whose 



advance of the greatest importance, j writings contain many original views, 



for the entire doctrine of the sense- ' which have in some instances since 



perceptions has since become the ' been independently put forward by 



scientific foundation of this doctrine, I other authorities. See his ' Physi- 



and is, in a certain sense, the em- ! ology of Common Life ' (1860, chap, 



pirical exposition of the theoretical 8) ; ' Problems of Life and Mind ' 



discussion of Kant on the nature j (vol. i. p. 135, 1874) ; ' Revue Philo- 



oi the intellectual process of the 

 human mind." Cf. also p. 584. 



3 ' Vortriige und lleden,' vol. i. p. 

 378 ; vol. ii. p. 181. 



4 This excessive appreciation of 

 Miiller's theory is, however, very 



sophique' (Paris, 1876, No. 2); 

 ' The Physical Basis of Mind ' (1877, 

 p. 184). Without knowing of Lewes's 

 criticisms, Prof. Wundt was led to 

 a criticism of the doctrine from 

 the physiological side in the first 



