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, ' Haiidbuch der ! much limited to Germany, and there 

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

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



2 Helmholtz, ' Vortrage und Re- Helmholtz is the central figure. In 



den,' vol. ii. p. 224 ; also ' Physiolo- 

 gische Optik,' p. 249 : " Miiller's law 

 of the specific energies marks an 

 advance of the greatest importance, 

 for the entire doctrine of the sense- 

 perceptions has since become the 

 scientific foundation of this doctrine, 

 and is, in a certain sense, the em- 

 pirical exposition of the theoretical 

 discussion of Kant on the nature 

 of the intellectual process of the 

 human mind." Cf. also p. 584. 



3 ' Vortrage und Reden,' vol. i. p. 

 378 ; vol. ii. p. 181. 



4 This excessive appreciation of 

 Miiller's theory is, however, very 



England the doctrine was subjected 

 to a full criticism by George Henry 

 Lewes, an important thinker, whose 

 writings contain many original views, 

 which have in some instances since 

 been independently put forward by 

 other authorities. See his ' Physi- 

 ology of Common Life ' (1860, chap. 

 8) ; ' Problems of Life and Mind ' 

 (vol. i. p. 135, 1874) ; ' Revue Philo- 

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

 ' The Physical Basis of Mind ' (1877, 

 p. 184). VVithoutknowing of Lewes's 

 criticisms, Prof. Wundt was led to 

 a criticism of the doctrine from 

 the physiological side in the first 



