162 PROGRESS OF SCIENCE IN THE CENTURY. 



symbolism of " lines of force," was re-expressed and 

 further developed in the sterner language of mathe- 

 matics by James Clerk Maxwell (1831-1879), who 

 was also led to conclude on theoretical grounds that 

 electro-magnetic phenomena and light phenomena are 

 alike due to waves of periodic displacement in the 

 same medium (the hypothetical ether), and are, in 

 fact, identical in nature. 



Hertz. — What Clerk Maxwell had theoretically 

 foreseen was experimentally demonstrated by Hein- 

 rich Rudolf Hertz (1857-1894), who detected the 

 electromagnetic (electric and magnetic) waves radi- 

 ating into space from the sparks of a Leyden jar or 

 of a Holtz machine, separated the two components, 

 electric and magnetic, and succeeding in reflecting, 

 refracting, diffracting, and polarising the waves. 

 " The object of these experiments,'' he says, " was 

 to test the fundamental hypothesis of the Faraday- 

 Maxwell theory, and the result of the experiments is 

 to confirm the fundamental hypotheses of the 

 theory." * As Hertz fully recognised. Professors 

 Oliver Lodge and G. F. Fitzgerald were about the 

 same time within sight of the same discovery of the 

 electro-magnetic waves in air. 



In a review of electrical advance in recent 

 years, Mr. Elihu Thomson notes that the work 

 of Hertz demonstrated " the fact that light of 

 all kinds and from all sources is really an electri- 

 cal phenomenon, differing from ordinary alternate- 

 current waves only in the rate of frequency of vibra- 

 tions. We produce electric waves of about one hun- 

 dred vibrations per second for alternating current 

 work ; and in the waves of red light the rapidity is as 



* Quoted by Cajori from Hertz's Electric Waves, trans. 

 by Dr. B, Jones, London, 1893. 



