xxix 



Helmholtz also developed the theory of electrical double layers at 

 the surfaces which separate two bodies of different potentials, and 

 applied the theory to the explanation of electrical convection and 

 other phenomena. 



His views on galvanic polarisation and electrolysis were expounded 

 in the Faraday Lecture, delivered before the Royal Institution in 

 1881. 



In the year 1886 he published a paper " On the Physical Meaning 

 of the Principle of Least Action." This was the first of a series in 

 which he extended the application of that principle to electro- 

 dynamics. 



His last paper was on this subject. It was communicated to the 

 Academy of Berlin on June 14, 1894, less than three months before 

 his death, and appears in his collected works as an unfinished 

 fragment. It is characteristic of the wide view which he took that 

 this final effort was an attempt to deduce the principles of electro- 

 dynamics, " von Maxwell aufgestellten, von H. Hertz ausfiihrlicher 

 formulirten," from a generalised form of the principle of least 

 action. 



An account of von Helmholtz would be incomplete without a 

 reference, however brief, to his philosophical views. 



He adhered to the opinion that our senses convey to us only 

 symbols of the truth. In an eloquent passage (' Wissenschaftliche 

 Abhandlungen,' ii, p. 608) he declared that the sensations of light 

 and colour have just as much and just as little relation to external 

 facts as the name, or even the handwriting, of a man have to the 

 man himself. The only difference between the symbolism of speech 

 and that of our senses is that the former is more or less arbitrary,. 

 w r hile the latter is a universal language, without dialects, which 

 nature prescribes. 



But von Helmholtz also held that our most fundamental concep- 

 tions are based not upon innate ideas, but upon the use of these 

 inexplicable sensations, conveyed to us by organs which, though they 

 tell us all we need to know, are from the instrument maker's point of 

 view imperfect. But while describing Kant's theory of the a priori 

 origin of the geometrical axioms as " eine unerwiesene," " un- 

 nothige," and " ganzlich unbrauchbare Hypothese," he gave greater 

 weight to the principles of mechanics, as enabling us to judge of the 

 relations of real things. As soon as these principles, he said, " are 

 conjoined with the axioms of geometry we obtained a system of pro- 

 positions which have real import If such a system were to 



be taken as a transcendental form of intuition and thought, a pre- 

 established harmony between form and reality must be assumed." 



These and various other points, both scientific and philosophical, 

 were discussed by von Helmholtz, not only in papers addressed to- 



