li)ll] on Radiotplefiraphy. 207 



Professor Zenncck* has carefully examined the effect of earthed 

 receiving and transmitting aerials, and has endeavoured to show mathe- 

 matically that when the lines of electrical force, constituting a wave 

 front, pass along a surface of low specific inductive capacity — such as 

 the earth — they become inclined forward, their lower ends being re- 

 tai'ded by the resistance of the conductor, to which they are attached. 

 It therefore would seem that wireless telegraphy as at present practised 

 is, to some extent at least, dependent on the conductivity of the earth, 

 and that the difference in operation across long distances of sea com- 

 jtared to over land is sufficiently explained by the fact that sea water 

 is a much better conductoi- than is land. 



Cli 



Fig. 13. 



The importance or utility of the earth connection has been some- 

 times questioned, but in my opinion no practical system of wireless 

 telegraphy exists where the instruments are not in some manner con- 

 nected to earth. By connection to earth I do not necessarily mean an 

 ordinary metallic connection as used for wire telegraphs. The earth 

 wire may have a condenser in series with it, or it may be connected 

 to what is really equivalent, a capacity area placed close to the surface 

 of the ground. It is now perfectly well known that a condenser, if 

 large enough, does not prevent the passage of high-frequency oscilla- 

 tions, and therefore in this case, when a so-called balancing capacity 

 is used, the antenna is for all practical purposes connected to earth. 



I am also of opinion that there is absolutely no foundation in the 

 statement which has recently been repeated to the effect that an earth 

 connection is detrimental to good tuning, provided of course that 

 the earth is good. 



Certainly, in consequence of its resistance, what electricians call a 

 bad earth will damp out the oscillations, and in that way make tuning 

 difficult ; but no such effect is noticed when employing an efficient 

 earth connection. 



In conclusion, I believe that I am not any too bold when I say that 

 wireless telegraphy is tending to revolutionise our means of communi- 

 cation from place to place on the earth's surface. For example, com- 



* " Annalen der Physik," xxiii., p. 846, " Physikalische Zeitschrift/' 1908, 

 pp. 50, 553. 



