DEVELOPMENTS IN TELEPHONY AND TELEGRAPHY JEWETT. 507 



RADIOTELEPHONY. 



While the foregoing comments on recent developments pertain 

 mainl}^ to radiotelegraphy, many of them apply equally to radio- 

 telephony. At the same time it can be said that up to within the 

 last year or 15 months very little of practical importance had been 

 done in the field of radiotelej)hony. 



During 15)15 very considerable progress has been made and us is 

 well known, successful radiotelephony has been carried on between 

 the Naval Radio Station at Arlington and such distant points as the 

 Isthmus of Panama, San Francisco, San Diego, Honolulu, and Paris. 

 An important part of this work has been a demonstration of the 

 practicability^ of directly connecting long-distance telephone and 

 telegraph wires to the radio system at either the transmitting or re- 

 ceiving end, thus making possible a continuous communication chan- 

 nel involving one or more wire and one or more radio links. 



The success of these recent improvements in long-distance radio- 

 telephony has been made possible not only by i^iprovements in the 

 receiving apparatus but more particularly by improvements in the 

 transmitting apparatus and in the means for influencing and modu- 

 lating the radiation of large amounts of energy from the antenna 

 sj^stem. 



APPARATUS FOR THE TROPICS. 



In a meeting such as a Pan American Scientific Congress, where 

 many of the delegates are interested in the conditions which obtain 

 in the Tropic^al Zone, no paper on recent developments in telephony 

 and telegraphy would be complete Avithout some mention of the 

 special developments that have been made to better the operation of 

 apparatus used in such localities. 



Roughly speaking, the conditions of telephone and telegraph oper- 

 ation which require special consideration in tropical countries are 

 those arising from: 



1. The higher temperature and higher average humidity which 

 obtains. 



2. The greater severity of lightning storms and other atmospheric 

 disturbances. 



3. The prevalance in some localities of insects which are peculiarly 

 destructive to wood, fabrics, and even to metals. 



Trouble in telephone plants from the first of these causes is espe- 

 cially noticeable wherever there is common battery operation. With 

 this system practically all parts of the local telephone plant are sub- 

 jected to the continuous application of the central office battery volt- 

 age. This, obviously, results in increased electrolytic corrosion 

 troubles where there is any chance of such action. 



