PROFESSOR IN BERLIN 293 



conductors, as had appeared from his own experiments on the 

 electric charges of the surface of rotating conductors in the 

 magnetic field. According to Faraday, dielectric polarization 

 must occur in all insulators lying between the conductors, 

 when the limiting conductors are charged electrically, and 

 must be of such intensity that the motion of the electricities 

 associated with the setting up of this condition may be re- 

 garded as the equivalent continuation of the electric current 

 with which the conductor is charged. Every current accord- 

 ingly must be a closed current, for which all the divergent 

 theories lead to the same result. It follows also that any 

 direct action of forces at a distance, which was still admitted, 

 must vanish in favour of alterations of dielectric and magnetic 

 strains in the ether-pervading space. 



' Every radical alteration of the fundamental principles and 

 postulates of a science/ said Helmholtz at a later time, 

 'necessarily involves the formation of new abstract concepts, 

 and unfamiliar associations of ideas, which the contemporary 

 student can only assimilate slowly, if he be inclined to take 

 the trouble of doing so at all. The import of a new abstraction 

 can only be understood clearly when its application to the 

 chief groups of individual cases which it comprises has been 

 thought out, and found valid. It is very hard to define new 

 abstractions in universal propositions, so as to avoid misunder- 

 standings of all kinds. It is, as a rule, much harder for the 

 creator of such a new idea to make out why others fail to 

 understand him, than it had been to discover the new truth. 

 I will not disparage Faraday's contemporaries, because his 

 words appeared to them uncertain and dark sayings. I re- 

 member too well how often I have sat gazing hopelessly at 

 one of his descriptions of lines of force, of their number and 

 tensions, or have sought to puzzle out the meaning of some 

 law in which the galvanic current is treated as an axis of force, 

 and so on. A Clerk Maxwell was required, a second man of 

 the same depth and independence of insight, to build up in the 

 normal forms of our systematic thinking the great structure 

 whose plan was present to Faraday's mind, which he saw clear 

 before him, and endeavoured to render apparent to his conr 

 temporaries/ 



Whatever Helmholtz's inclination to support the views of 



