c= 



:nSY 







2tt 



V 





T ' 



V 2 





4000 



irV 



of Ether Waves in Air. 775 



To see what G = en means. Write e = $Y. 



Let S be comparable to KZ' 5 that is let it correspond to a 



•capacity area not greatly differing from the height of the 



aerial in linear dimensions, and let V correspond say to 



nearly an inch spark, say 60,000 volts or 200 electrostatic 



units. Then 



200 v magnetic units 



— amperes. 



A, 



If V is 200 metres and X = 4 kilometres, C = 600 amperes. 



It is noteworthy, though now familiar, how strong a current 

 amplitude is readily produced by a disruptive discharge. 



Arguments for use of long waves. 



Although short waves have so many advantages, they need 

 not be as efficient as long ones at really great distances if 

 they have to overcome obstructions or opacities in the 

 atmosphere. For when it comes to transmitting waves near 

 the surface of the earth, the simple theory of unimpeded 

 etherial transmission is no longer sufficient. Earth con- 

 duction and air conduction become of the essence of the 

 phenomenon, and many complications may happen to the 

 waves, some of which have attracted the attention of mathe- 

 maticians — notably at present Professor Zenneck, who has 

 dealt elaborately with the problem of earth and sea con- 

 duction in his important paper in the Annalen der Physik, 

 vol. xxiii. page 846, 1907; summarised or translated by Pro- 

 fessor Fleming in 'Engineering' for June 4th and 11th, 

 1909, and also in the 1910 edition of his book. His treat- 

 ment of the effect of earth-surface conductivity seems very 

 thorough, hut as regards the effect of aerial conductivity our 

 knowledge is still slight. 



The reason of the observed obstructive influence of sun- 

 shine is not yet clearly known ; but if the opacity of ordinary 

 air due to observed ionization is calculated from recognized 

 data, it appears to be by no means sufficient to account for 

 the observed effect by simple obstruction : though the sur- 

 prisingly high conductivity of rarefied air in the absence of 

 electrodes must not be forgotten. 



On the whole it seems probable that the difficulty of trans- 

 mission by day must be due to something happening in the 

 upper conducting layer of the atmosphere. I assume that 

 grazing reflexion from this layer must usually assist trans- 

 mission. If the transition of density is sudden, the layer will 



3G2 



