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nexion with Hertz's work, to call attention 1 to 

 old experiments, and ideas taken from them, by 

 Joseph Henry, which came more nearly to an 

 experimental demonstration of electromagnetic 

 waves than anything that had been done pre- 

 viously. Indeed Henry, after describing experi- 

 ments showing powerful enough induction due to 

 a single spark from the prime conductor of an 

 electric machine to magnetise steel needles at a 

 distance of thirty feet in a cellar beneath with two 

 floors and ceilings intervening, says that he is " dis- 

 posed to adopt the hypothesis of an electrical plenum," 

 and concludes with a short reviewing sentence : 

 " It may be further inferred that the diffusion of 

 " motion in this case is almost comparable with 

 " that of a spark from a flint and steel in the case 

 " of light." 



Professor Oliver Lodge himself did admirable 

 work in his investigations with reference to light- 

 ning rods,' 2 coming very near to experimental 

 demonstrations of electromagnetic waves ; and he 



1 Modern Views of Electricity, pp. 369372. 

 - 2 Lightning Conductors and Lightning Guards, Oliver J. Lodge, 

 D.Sc., F.R.S. Whittaker and Co. 



