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assumption of space being void, and conjectured that the ether 

 which transmits the luminous waves suffers modifications per- 

 ceived under the form of electrical and magnetic manifestations. 

 His discoveries, important as they were, gained due consideration 

 only when Faraday's great countryman. Maxwell, treated the 

 same subject in a purely scientific and theoretical way, publish- 

 ing in 18G5 his Mathematical Theory of Light. The nature and 

 properties of ether he left undecided, and they form to this day 

 dominant questions, destined, it seems, ultimately to reveal the 

 deepest secrets of natural science. Maxwell labored to confirm 

 the connection, surmised by Faraday, between light, electricity, 

 and magnetism ; the idea of velocity now entered the theory and 

 became of supreme importance. Maxwell arrived at the conclu- 

 sion that the velocity of electromotion in a given medium must 

 be identical with the velocity of light in the same medium, and 

 that therefore ether, being contained in all ponderable bodies, 

 would have to be looked upon as the conductor of electric motion 

 and power. Consequently the periodical motions of ether, which 

 our eye conceives as light, and which he figured as transversal 

 waves, were considered by Maxwell to be at the same time undula- 

 tions of electricity. These conceptions, unproved by experiment 

 as Maxwell left them, had merely the value of a scientific hy- 

 pothesis emanating from a man of rare genius. To have proved 

 them facts, and thereby to have united two vast and highly im- 

 portant domains of natural philosophy, is the lasting credit of 

 Prof. Hertz. 



The complexity of phenomena of light and electricity and the 

 insufficient opportunities afforded by the laboratory for deduc- 

 tions of such magnitude rendered the obstacles barring the road 

 to exact observation well-nigh insurmountable. Many of the best 

 and ablest naturalists were laboring to cope with these difficul- 

 ties. Two English scientists of highest standing. Prof. G. F. Fitz- 

 gerald and Dr. O. T. Lodge, were during the eighties occupied 

 with experiments for the investigation and measurement of elec- 

 tric waves. But it was reserved for Hertz to discover and apply 

 with marvelous ingenuity the necessary " detector,'' a resonating 

 circuit with an air-gap, the resistance of which is broken down 

 by well-timed impulses, so that visible sparks are produced. 

 After an unceasing course of experiments, in which he mani- 

 fested indefatigable energy and a wonderful faculty of reaching 

 the very essence of the matter, he succeeded in deciding the ques- 

 tions: Is the propagation of electrical and magnetic forces in- 

 stantaneous ? and further : Can electrical or magnetic effects be 

 obtained directly from light ? The paper On very Rapid Electric 

 Oscillations, which was published in 1887, was the first of a 

 splendid series of researches which appeared in Wiedemann's 



