HELMHOLTZ IN BERLIN 



his son, C. Neumann, Riemann, Grassmann, and 

 Clausius. According to Helmholtz, the field of 

 electrodynamics was at this time a pathless desert. 

 ('So war das Gebiet der Elektrodynamik um jene 

 Zeit zu einer unwegsamen Wiiste geworden.') l 

 The theory of electrical action at a distance gave 

 little satisfaction. 



Then arose the conception that actions between 

 electrified bodies occupied time and required an in- 

 tervening medium. The turning-point between the 

 old and the new conceptions was reached in 1837, 

 when Faraday published his experiments on the 

 specific inductive capacity of substances. Faraday 

 proved that the force of repulsion between two similar 

 quantities of electricity depends not only on the 

 quantities and on their distance apart, but also on the 

 intervening medium. 2 The English philosopher had 

 a genius for experiment, and he was guided by a 

 marvellous insight into hidden processes. As has 

 been well said by Clerk Maxwell, ' Faraday, in his 

 mind's eye, saw lines of force traversing all space, 

 where the mathematicians saw centres of force 

 attracting at a distance ; Faraday saw a medium 

 where they saw nothing but distance ; Faraday sought 

 the seat of the phenomena in real actions going on 

 in the medium, they were satisfied that they had 



1 Introduction by Helmholtz to Die Primsifien der Mechanik, von 

 Heinrich Hertz, s. xi. 



2 An excellent account of electrical units is given by Magnus Maclean 

 in his work on Physical Units. London, 1896. 



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