254 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1913. 



In the antenna transmission just considered it is assumed that the 

 surface of the earth is, generally speaking, a good electric conductor. 

 The surface of the sea is sufficiently good. Dry land surface, how- 

 ever, is not a good conducting sheet, and even though moist it is 

 generally so irregularly conducting that obliteration of the waves 

 and loss or absorption of the energy must necessarily occur. Obsta- 

 cles, such as dry rock ranges, may absolutely prevent the waves from 

 passing over them. It must be borne in mind that these waves have 

 no inertia, as such, and that the energy must be guided to its desti- 

 nation by a conducting sheet. This calls to mind the efforts that 

 were made to connect Lynn and Schenectady by a wireless system, 

 but without success. Occasionally signals were received, but in gen- 

 eral they were too indistinct to be recognized. It is more than 

 probable that the dry rock ranges of the Berkshires in western 

 Massachusetts were sufficient of an obstacle to prevent the energy of 

 the waves getting across them. 



It is also to be questioned whether there may not be another action 

 which interferes with and disturbs the integrity of the waves. It is 

 conceivable that waves may follow a water surface, even around a 

 cape, and that a portion of the energy may take a short cut across 

 the land of the cape. If this be so, the longer course would be 

 around the cape, the shorter course across the land. The wave 

 lengths would remain the same, and an out-of-phase relation or 

 interference phenomenon would take place to a greater or less extent. 

 It is manifestly necessary that the energy, by whatever course it fol- 

 lows, shall reach the receiving apparatus in phase. 



Let us now consider for a moment the conditions at great dis- 

 tances over the earth's surface. At moderate distances from the trans- 

 mitting antenna the surface may be considered as flat. The conducting 

 sheet guiding the energy is flat or plane, but at great distances the 

 curvature of the earth's surface becomes an important factor. For a 

 time there was a great deal of discussion as to the reason why the energy 

 in the wireless transmission seemed actually to follow the curvature of 

 the earth, instead of going straight away, as in the case of Hertzian or 

 heat and light waves. If the waves had been generated by a large 

 Hertzian oscillator, it would not be possible for them to so follow 

 the earth's curvature, but inasmuch as they are in wireless work 

 produced and, as it were, positioned upon a conducting sheet (the 

 sea surface) , then it follows that the energy must be guided by that 

 conducting sheet or surface, regardless of its extent or its curvature. 

 I have never been able to understand why so much discussion has 

 been needed to clear up this point. Wireless waves have no inertia — 

 they follow the course of the charges which produce the stress and 

 of the magnetic field, due to these charges in motion. These charges 

 in motion are the currents in the conducting sheet, which may or 



