XXY111 



the conservation of energy in the sense that two electrified particles 

 starting with a finite velocity would within a finite distance acquire 

 infinite speed, and therefore infinite energy. 



An account of the controversy which followed on the publication 

 of this view has been given by Maxwell. It is, therefore, sufficient 

 to say that Helmholtz maintained his position against all attacks. 



It remained, however, to discuss the case when h was equal to or 

 greater than zero. The most interesting part of this investigation 

 was the application of the generalised formula to the propagation of 

 electrical and magnetic disturbances through bodies capable of 

 electrical or magnetic polarisation. These properties were treated 

 independently. The conclusions arrived at may be summed up as 

 follows. 



Both longitudinal and transversal electric disturbances can be 

 propagated in unmagnetisable dielectrics. The velocity of the trans- 

 versal undulations in air depends on the absolute susceptibility of the 

 medium. If this is very large the velocity is the same as that of 

 light. The velocity of the longitudinal waves is equal to that of the 

 transversal waves multiplied by the factor ij^h and by a constant 

 which depends on the magnetic constitution of the air. In con- 

 ductors the waves are rapidly damped. If the insulator is magnetis- 

 able, the magnetic longitudinal oscillations have an infinite velocity, 

 the transversal magnetic oscillations are perpendicular to the trans- 

 versal electrical oscillations, and are propagated with the same 

 velocity. 



In the particular cases when k = the longitudinal waves of 

 electricity have also an infinite velocity, and the theory is then in 

 close accord with that of Maxwell, provided that the absolute specific 

 inductive capacity of the air is great enough to make the common 

 velocity of the electrical and magnetic transversal undulations equal 

 to that of light. 



The paper, of which an account has just been given, was entitled 

 " On the Equations of Motion of Electricity in Conductors at Rest," 

 and was described by Maxwell as "very powerful." It was followed 

 four years later (1874) by a memoir, in which the theory was applied 

 to conductors in motion, and by several others of a more or less 

 controversial character. 



An interesting result of the attention given by Helmholtz to the 

 theory of electricity was a series of experiments, carried out in his 

 laboratory by Professor Rowland, to determine whether the magnetic 

 effects of an electric current were identical with those produced by 

 the displacement of matter carrying an electrostatic charge. As 

 these experiments were planned by Rowland, it must suffice to state 

 that it was proved that a revolving charged conductor behaves like a 

 ring-shaped electric current. 



