HERMANN VON HELMHOLTZ 



mensely greater than that of light, varying from 

 decimetres to kilometres, while the waves that fall on 

 the retina, and constitute what we call light, have a 

 wave-length of only from 0*3 to 0-7 thousandths of a 

 millimetre. 1 Then, by the principle of ' resonance,' 

 (using this word in a special sense), the waves may 

 be detected as minute sparks, or by acting on an 

 arrangement called a coherer. 2 Hence wireless tele- 

 graphy ! 



Hertz always referred the inspiration to Helmholtz, 

 and W. von Bezold gives his impression of the 

 memorable occasion when Helmholtz reported to the 

 Academy on the researches of his distinguished pupil. 

 'The impression will never be forgotten by any- 

 one. . . . The most intense and purest joy shone in 

 the countenance of the great master, who explained in 

 eloquent words, and with the freshness of youth, the 

 importance and influence of this fundamental work.' 

 This was in 1888. Six years later, on the ist of 

 January 1894, Hertz died before the completion of 

 his thirty-seventh year. Helmholtz wrote of him 

 these words : c The news of the death of this 

 favourite of genius was a severe shock to all who 



1 Relation between British and metric units of length and mass : 

 i yard = o'9i439i79 metre; i metres 1*09362311 yards = 39*370432 

 inches; i poundzzo'453593 kilogramme; i kilogrammes 2*2046212 

 pounds; also, i kilometre = 1000 metres; i millimetre ToVrjth 

 metre = 5*jth inch. 



2 Kerr. Wireless Telegraphy. London, 1898. Also, Andrew Gray's 

 Treatise on Electricity and Magnetism, vol. i.. London, 1898, chap, xi., 

 for a full description of the Hertzian Vibrator and Receiver. 



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