IV- 



of Ether Waves in Air. 785* 



expected to sweep away the charged corpuscles which it 

 encounters and to leave a clear space. 



To get an idea o£ the magnitude of this influence of a 

 Hertz vibrator, take a straight vertical one of electric- 

 moment Ql with a current amplitude in it C =2ttQ/T. The 

 magnetic field at any distance r (greater than say half a 

 wave-length) is 



H= -^-^cos 6 . sin (qr—pt), 



where 6 is the inclination to the horizon (the latitude, so to 

 speak). So on the " equator " the magnetic amplitude is 



4tt 2 Q? 27tC Z 

 110 ~ T\r - Xr ' 



Hence the velocity acquired by the particles, 



fp ^y (\H ) 2 



\477 m) v 



= ll.(l) 2 ( ( k 1 \ 2 . 



4zV \mj \ r J 



So the speed generated in an electron by an upright Hertz 

 radiator, at a distance 10 times the height of the aerial 

 along its equator, will be comparable to a kilometre per 

 second if the mean aerial current is 600 amperes. The 

 velocity thus generated naturally falls off with the square 

 of the distance, just as the wave-energy does. 



The mere propulsion of a set of particles will not appre- 

 ciably consume the energy of a wave, provided the particles 

 remain individually the same and continue free, for electrons 

 steadily on the run would not contribute to opacity*. Under 

 the influence of Hertzian waves they would either be driven 

 into the atoms, or else would speedily acquire a terminal 

 velocity and be swept out of the way. The process suggests 

 a curious method of clearing; the air of electric charges ;. 

 and there may be some application of long electric waves for 

 this purpose. Assuming that ions in the atmosphere must 

 have some meteorological influence, it would seem just 

 possible that an indirect ether-wave effect on the weather,, 

 such as cranks have anticipated as likely to be due to wireless 

 telegraphy, may not be so absurd as at first sight it appeared. 



But passing this for the moment, and returning to the 



* See, however, the suggestion of Professor Poynting, referred to 

 on page 784. 



