ON THE PSYCHO-PHYSICAL VIEW OF NATURE. 485 



terminal organ, the connecting fibre or nerve, and the 

 central or percipient organ situated somewhere in the 

 brain. How are these different parts of the combined 

 apparatus anatomically constituted, and what are their 

 respective physiological functions in particular, where 

 does the specific energy reside ? The answer to these 

 questions as regards not only the process of seeing, but 

 likewise that going on in other sense organs, involved 

 an enormous amount of detailed anatomical and physio- 

 logical, analysing and experimenting work. With this 

 work many great names are connected first of all, 

 Helmholtz, who in his two great treatises on ' Physio- 

 logical Optics ' and ' Physiological Acoustics,' l has laid 

 the foundation of those two psycho-physical sciences 

 which bring us nearest to an understanding of the inter- 

 action of mind and body. Like Young before him, for 

 whom he expresses the greatest admiration, Helmholtz 

 had approached the study of nature from the side of 

 medicine : from this he was, by the peculiarity of his 

 genius, driven to mathematico-physical studies on the 

 one side, to psychological on the other. The exact 

 methods of the mathematical, the experimental methods 

 of the medical sciences ; the mental analysis of Kant 

 and Fichte, as well as the logical methods of J. S. 

 Mill, were equally familiar to him. Inventions of his 

 own, like that of the eye-mirror, or of others, like 



14. 



Helmholtz. 



1 ' Die Lehre von den Tonemp- 

 finduugen ; Physiologische Grund- 

 lage fiir die Theorie der Musik,' 

 1st ed., 1863. ' Handbuch der 

 physiologischen Optik,' 1867, 2nd 

 ed., much enlarged. A succinct 

 and very lucid exposition of the 



principal contents of those two 

 great treatises, by an authority in 

 the same domain of science, will be 

 found in chaps, x. to xii. of Prof. 

 J. Q. M'Kendrick's volume in the 

 " Masters of Medicine " Series on 

 H. von Helmholtz, 1899. 



