90 



in which the work of the past has been repudiated and destroyed and a 

 new order of things established. I mean that some of our ideas have 

 undergone such a complete and rapid change that what some might term 

 an evolution is really a revolution. Indeed, we have had two revolutionary 

 periods within the life of this Academy. 



The first came in 1887 with the epoch-making researches of Heinrich 

 Hertz. Faraday had given us his theory of lines of force and the mathe- 

 maticians had attacked it. Young and Fresnel had given us the undu- 

 latory theory of light and Laplace and Poisson had "befuddled us with 

 their objections." Ampere had given a theory of magnetism, but Poisson 

 and Weber had given two others. To explain an electric charge we could 

 resort to the one-fluid theory, the two-fluid theory, the potential theory, 

 the energy theory, the ether-strain theory. Maxwell had written a treatise 

 on electricity which few could read and no one could fully understand. A 

 distinguished French physicist said he understood everything in Maxwell's 

 book except what was meant by a body charged with electricity. Max- 

 well had given us but a vague idea of electric displacements and displace- 

 ment currents, because his ideas were bound up in equations without ex- 

 perimental verification, or even illustration. 



Then came Hertz's researches, which confirmed the fundamental hy- 

 potheses of the Faraday-Maxwell theory and "annexed to the domain of 

 electricity the territory of light end radiant heat." lu Many thinkers," said 

 Lord Kelvin, "have helped to build up the nineteenth century school of 

 plenum, one ether for light, heat, electricity and magnetism ; and Hertz's 

 electrical papers, given, to the world in the last decade of the century, will 

 be a permanent monument of the splendid consummation now realized." 

 Some one has said that Hertz enthroned Maxwell in every chair of- physics 

 in Europe and America. 



It appears that many of the ancient philosophers had a shadowy idea 

 of a medium in space which they personified and called "Aether." Ac- 

 cording to Heriod, Aether was the son of Erebus and Night and the brother 

 of Day. The Orphic hymns speak of Aether as the soul of the world, the 

 animator of all things, the principle of life. The children of Aether and 

 Day were the objects about us, the heavens with all their stars, the land, 

 the sea. Aether was the lightest and most active form of matter and Day 

 had the power of converting it into heavier matter. Plato speaks of the 



'Kelvin. Introduction to Jones' translation of Hertz's "Electric Waves." Macmil- 

 1 an, 1893. 



