xi ACROSS THE BORDER 295 



discharge of a Leyden jar or other form of electric con- 

 denser, the spark is not due to a single splash of electricity 

 from one point to another, but to many rapid oscillations 

 of electric action between the two points. The total 

 duration of the discharge is far too short to be analysed 

 by the eye, but if it could be extended over a sufficiently 

 long interval the spark would be seen swinging like a 

 pendulum from one point to the other until the surging 

 disturbance which produced it had settled down again. 

 Both Lord Kelvin and von Helmholtz independently 

 reached the conclusion expressed by Henry before them 

 as to the oscillatory character of the electric discharge ; 

 and Clerk Maxwell showed that such a discharge must 

 give rise to etheric disturbances which would travel 

 through space with the velocity of light. 



When a theory can be stated in mathematical terms 

 it is possible to predict effects before they are actually 

 observed. The consequences of Maxwell's theory were 

 clearly understood by physicists, two of whom, Prof. 

 Heinrich Rudolf Hertz in Germany, and Sir Oliver 

 Lodge in England, devoted themselves to the task of 

 detecting the ether waves which must be created by an 

 oscillatory electric discharge. About 1888 Maxwell's 

 prophetic conclusions were brought within the range of 

 demonstration by Hertz, who discovered a means of 

 increasing the amplitude of the electric waves radiated 

 from the discharge circuit, and devised a sensitive 

 detector of these periodic disturbances of the ether. 

 It was Hertz, therefore, who provided the experimental 

 proof for which science had waited twenty years. 



The difference between light waves and electric waves 

 now called Hertzian waves in honour of their discoverer 

 is a difference in length, or of rate of vibration of the 

 ether. The shortest waves which affect our sight are 



