PREFACE v 



theories of electricity had been noticed and rejected 

 by Faraday and Maxwell, and probably by many 

 other philosophers and workers ; but certainly accepted 

 by none. Now in the beginning of the twentieth 

 century we all believe that electricity consists of atoms. 

 How far-reaching is this theory, and how much science 

 is enriched by it, is splendidly illustrated by Becquerel's 

 discovery of radio-activity, and the magnificent harvests 

 of new and astonishing truth which have been 

 gathered by the numerous and brilliant workers in 

 the field of investigation thus opened to the world. 



I cannot conclude this short preface without re- 

 ferring to the great debt which the world owes to 

 Helmholtz, in having given to Hertz the inspiration 

 to find experimental proof of Maxwell's electric waves ; 

 and giving him, in the Physical Institute of the 

 University of Berlin, the apparatus and appliances by 

 means of which he carried out the investigation. To 

 this we owe the first practical demonstration of pro- 

 gressive electric waves, and of stationary waves, in 

 air, and therefore inferentially in ether undisturbed 

 by ponderable matter. Thus in Helmholtz we find 

 a prime factor in the grand series of theoretical and 

 experimental researches through which wireless tele- 

 graphy has been achieved. 



The Oxford University Press has earned the grati- 

 tude of all English-speaking scientific workers in 

 giving to them this English version of the very 

 valuable and interesting Life of Helmholtz, by 

 Dr. Kdnigsberger. 



KELVIN. 



