362 GREAT MEN OF SCIENCE 



of waves in wires was successful, the waves being made 

 stationary in exactly the same way as is possible with waves 

 in ropes or water, or with sound waves, by reflecting them 

 back upon themselves; this is very simply accomplished in 

 the case of electric waves in wires, by insulating the ends of 

 the wires. Hertz was then able to demonstrate the presence 

 of nodes and loops of electric force in the wires by means of 

 tiny sparks, and double the distance from one node to the 

 next gave, as in the case of all stationary waves, the wave 

 length. 



He then also succeeded in producing stationary waves of 

 this kind without wires in free space between the oscillator 

 and a reflecting wall, and likewise in measuring their wave- 

 length. The equality of the wave-length with that found in 

 wires would indicate an equal rate of propagation in the two 

 cases, that is to say the velocity of light predicted by Maxwell. 

 This important demonstration was a matter of some diffi- 

 culty for Hertz, since the space available to him was too 

 small for an undisturbed development of the waves; this 

 proof only succeeded somewhat later (1893) when the ex- 

 periments were repeated in a large hall.^ A metallically 

 conducting wall proved to be suitable for reflecting the 

 waves, which also agreed with Maxwell's theory. We then 

 have a node of electric force on the wall itself; no spark is 

 there exhibited by the resonator. At the loops, where the 

 sparks appear, the transverse nature of the waves can be 

 proved; the electric force is at right angles to the direction of 

 propagation of the waves. It was then also possible to study 

 satisfactorily the waves freely radiated from the oscillator by 

 means of the resonator, and compare them with the effects 

 predicted by Maxwell's equation, full agreement being 

 found. 



1 A full account of these investigations by Hertz himself is to be found 

 in his work Electric Waves, translated by D. E. Jones, with an introduction 

 by Lord Kelvin, London, 1893 and 1900. See also his Miscellaneous 

 Pa/)er5, translated by D. E. Jones and G. A. Schott, London, 1896. 



