HELMHOLTZ IN BERLIN 



Is there anything analogous in magneto-electric 

 action ? Fitzgerald was the first to suggest an 

 attempt to measure the length of electric waves ; 

 and Helmholtz propounded the question for a prize 

 essay to be awarded by the Berlin Academy. 



It was reserved for Hertz, the favourite pupil of 

 Helmholtz, to prove the correctness of Clerk 

 Maxwell's theory, and actually to demonstrate the 

 existence of electro-magnetic waves, or, as they are 

 usually called, the Hertzian Waves. How he 

 was led step by step to this great discovery, over- 

 coming difficulties as they arose, and going into this 

 unknown land in the firm belief that scientific theory 

 would not lead him astray, has been fully described 

 by Hertz himself. 1 He showed that waves of electric 

 energy consist of displacements transverse to the direc- 

 tion of transmission, and are governed by the same 

 laws of reflection, refraction, and polarisation as those 

 of light. Their velocity of transmission is the same as 

 that of light, 300,000 kilometres per second (186,380 

 miles per second, in vacuo ; Michelson, 1879). As 

 the electric oscillations produced by the Hertzian 

 method are comparatively few in number per second, 

 when the velocity of light is divided by this number, 

 the resultant wave-length is still found to be im- 



1 Hertz. Electric ffa-ves. Trans, by Jones, with preface by Lord 

 Kelvin. London, 1893. See especially the Introduction, p. I. See also 

 a lecture by Hertz On the Relations bet-ween Light and Electricity, delivered 

 on Sept. 20, 1889, and printed in his Miscellaneous Papers, trans, by 

 Jones, p. 313. London, 1896. 



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