36o GREAT MEN OF SCIENCE 



way taken by Hertz, and leave out of consideration previous 

 reconnaissances . 



The meaning of Maxwell's equations showed that the 

 electric waves in question must proceed from electric oscilla- 

 tions, which W. Thomson (Lord Kelvin) had already taught 

 us how to calculate in every respect, and the production of 

 which had already been proved, for example in the discharge 

 of Leyden jars. In experiments with the discharge of jars, 

 the periodicity of the oscillations had been measured, by 

 observing the discharge spark in a rotating mirror, whereby 

 it was clearly seen that at every discharge a number of sparks 

 passed to and fro, the intervals between these being half the 

 period of oscillation of the discharge; this period could thus 

 be measured. These frequencies might amount to hundreds 

 of thousands a second. 



If the transverse waves imagined by Maxwell proceed 

 from these oscillations, and are propagated with the speed 

 of light into space, the length of the waves - measured from 

 crest to crest - would be easily calculated in the manner ren- 

 dered clear by Newton for all waves, from velocity of propa- 

 gation and frequency; they would be measured in miles, and 

 this was much too long, not only as compared with the space 

 in which the waves could be tested for and investigated; but 

 also because the energy available in the discharge generating 

 the waves was not nearly sufficient to allow any perceptible 

 effect to take place, in view of the diminution of intensity 

 with distance, over a range of miles; thus it was not possible 

 to generate even a single such wave with an intensity suffi- 

 cient to allow it to be detected. 



This shows that, in order to render such waves perceptible, 

 it would be necessary to generate much more rapid oscilla- 

 tions than those hitherto studied; for the wave-length 

 changes inversely as the frequency. These more rapid 

 oscillations were to be expected, according to Lord Kelvin's 

 calculation, in the case of the discharge of smaller capacities 



