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 tho 

 electromagnetic (electric and magnetic) waves radi- 

 ating into space from the sparks of a Ley den jar or 

 of a Holtz machine, separated the two components, 

 electric and magnetic, and succeeded 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. 

 Ly Dr. E. Jones, London, 1893. 



