CHAPTER XVII 



THE PHILOSOPHICAL POSITION OF HELMHOLTZ 



TO understand the position of Helmholtz, with 

 regard to the great questions in philosophy, 

 we must take into account the school in which he 

 was trained and the path which he chose for himself in 

 physiological investigation. No physiological principle 

 influenced him so much as that of the specific energy 

 of nerves, taught by Johannes Miiller. The statement 

 of this principle is, that in whatever way a terminal 

 organ of sense may be stimulated, the result in con- 

 sciousness is always of the same kind. Thus the 

 vibrations of the ether that constitute physical light, 

 or pressure, or electrical stimulation, all cause, when 

 applied to the retina or to the optic nerve, sensations 

 of luminosity. The same is true of all the sense 

 organs. It is evident, therefore, that there is no 

 correspondence between the sensation and the physical 

 nature of the stimulus arousing it, seeing that the 

 latter may be varied while the former remains un- 

 altered. This principle was the guide to Helmholtz 

 in all his physiological work on the senses, just as that 

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