DEVELOPMENTS IN TELEPHONY AND TELEGRAPHY JEWETT. 505 



struction has been toward the use of larger antenna structures at the 

 sending station with a corresponding lengthening of the most effi- 

 cient wave length to be used. Although present knowledge is still 

 very meager, this tendency to large antenna systems at the sending 

 station is the result of the general experience in long-distance radio- 

 transmission, which appears to show that the lower frequencies, that 

 is, the longer wave lengths, are more readily and efficiently trans- 

 mitted than the higher frequencies or shorter wave lengths. 



For receiving, the use of amplifying devices has permitted the 

 adoption of very cheap and simple structures. Experience has 

 shown that the reduction in receiving efficiency by the adoption of 

 small antenna systems is compensated for by the reduction in atmos- 

 pheric disturbances — this making possible the use of a high degree of 

 amplification of tlie received signals. 



TRANSMISSION. 



The most important data on the laws governing the strength of 

 received signals which has been published during the last few years 

 are those obtained by Dr. Austin, of the United States Navy Depart- 

 ment. This data was in process of being augmented by a compre- 

 hensive series of simultaneous observations at widely separated sta- 

 tions under the direction of an international organization at the time 

 present hostilities in Europe commenced. Until such international 

 cooperation can be reestablished little of value is likely to be done. 



RECEIVING APPARATUS. 



As inferred above, the sensitiveness of receiving apparatus has 

 been very greatly increased during the past few years. This has 

 been accomplished largely through the employment of detectors of 

 the so-called Fleming, De Forrest, and Von Lieben types, together 

 with the use of locally generated oscillation methods of receiving 

 continuous wave-train signals. The introduction of continuous wave- 

 train systems and the improvements made in spark-sending appa- 

 ratus have also miade possible a decided increase in selectivity at 

 the receiving stations. 



ATMOSPHERIC AND INTERFERENCE DISTURBANCES. 



Although so-called atmospheric disturbances and interference 

 from other radio stations have always been recognized as one of the 

 serious limitations to the successful employment of radio and 

 although a vast amount of labor has been expended during the past 

 four or five years, the actual progress toward better conditions has 

 been relatively small. 



