274 HERMANN VON HELMHOLTZ 



media. 'His ideas were clothed in an abstract language 

 difficult to follow, and made but little way, until they found 

 their interpreter in Clerk Maxwell/ On this hypothesis there 

 were no open currents, since the accumulation of the electric 

 charges at the ends of the conductors, and consequent di- 

 electric polarization of the intervening insulators, represented 

 an equivalent electrical motion in the insulators, and it was 

 in this that Helmholtz recognized the cogency of Faraday's 

 views. 



Helmholtz then, ' in view of the immense significance which 

 this result may have in the further development of physics, 

 and because the question of the rate of transmission of 

 electrical action has recently been raised in many directions/ 

 set himself the task of investigating the results of the law of 

 induction as generalized by himself, in the presence of 

 magnetizable and dielectrically polarizable media. The dis- 

 cussion of the equations of motion of electricity, transformed 

 in view of dielectric polarization, led him, without adopting the 

 particular form of Clerk Maxwell's hypothesis, and while retain- 

 ing the idea of electrical action at a distance, to the same results 

 as Maxwell, i. e. that for a very large capacity of polarization 

 the velocity of the transverse waves is equal to the velocity of 

 light, while for a very small capacity it is infinitely great. The 

 velocity of the longitudinal waves in air is found, however, to 

 be directly proportional to that of the transverse, and indirectly 

 proportional to the square root of the constant k, so that for 

 k=o the assumption made in Clerk Maxwell's theory is con- 

 firmed, that the rate of transmission of the longitudinal 

 electrical waves is infinite, i.e. that there are no longitudinal 

 waves. Further conclusions as to the velocities of the transverse 

 and electrical longitudinal waves in other insulators harmonized 

 equally well with the theory advanced by Clerk Maxwell. 



In this first treatise on electrodynamics Helmholtz com- 

 pletely fulfilled his primary object, of sifting and clearing up 

 the opinions and methods already obtaining. 



At the beginning of the year 1870 Helmholtz, with Kirchhoff, 

 received the great distinction of being elected an external 

 member of the Academy at Berlin ; at the same time an event 

 occurred in the Berlin University, which was to have the most 

 important consequences to his career. 



