PRESIDENTIAL ADDRESSES. 543 



tion of magnetic waves to which he was led, that he 

 began his electric researches in a problem happily 

 put before him thirteen years ago by Professor 

 von Helmholtz, of which the object was to find by 

 experiment some relation between electromagnetic 

 forces and dielectric polarisation of insulators, 

 without, in the first place, any idea of discovering 

 a progressive propagation of those forces through 

 space. 



It was by sheer perseverance in philosophical 

 experimenting that Hertz was led to discover a 

 finite velocity of propagation of electromagnetic 

 action, and then to pass on to electromagnetic 

 waves in air and their reflection, and to be able to 

 say, as he says in a short reviewing sentence at the 

 end of his eighth paper : " Certainly it is a fasci- 

 " nating idea that the processes in air which we 

 "have been investigating, represent to us on a 

 " million-fold larger scale the same processes 

 " which go on in the neighbourhood of a Fresnel 

 "mirror, or between the glass plates used for 

 " exhibiting Newton's rings." 



Professor Oliver Lodge has done well, in con- 



