no 



POPULAR SCIENCE MONTHLY. 



atoms of the earth, and that when one electron enters an atom, another 

 leaves it. Hence corresponding to the electric wave in the space above, 

 there are electrical changes in the ground beneath. This view is con- 

 firmed by the well-known fact that the achievement of Hertzian wave 

 telegraphy is much dependent on the nature of the surface over which 

 it is conducted, and can be carried on more easily over good conducting 

 material, like sea water, than over badly conducting dry land. 





+ + + +• e 



m 



Fig. 7. Successive stages in the production of a Semi-loop of Electric Strain by a 

 Marconi Aerial Radiator. 



The matter may be viewed, however, from another standpoint. 

 Good conductors are opaque to Hertzian waves; in other words, are 

 non-absorptive. The energy of the electric wave is not so rapidly 

 absorbed when it glides over a sea surface as when it is passing over a 

 surface which is an indifferent conductor, like dry land. In fact, it is 

 possible by the improvement of the signals to detect a heavy fall of 

 rain in the space between two stations separated only by dry land. It 

 is, however, clear that on the electronic theory the progression of the 

 lines of electric strain can only take place if the surface over which 

 they move is a fairly good conductor, unless these lines of strain form 

 completely closed loops. Hence we may sum up by saying that there 

 are three sets of phenomena to which we must pay attention in formu- 



