476 BELL SYSTEAT TECHNICAL JOURNAL 



interference, and consist of the use of synchronous motors, rectifiers 

 and specially designed filters, together with the locating of the ap- 

 paratus and wiring in such a way as to effect a minimum coupling 

 between the teletypewriter and its associated loop and the radio antenna 

 system. 



Conclusion 



History of air transportation in the past few years indicates that 

 continued growth may be expected, particularly as hazards to flying 

 are mitigated and safety and dependability are recognized by the 

 public. The Government is continuing the extension of airways and 

 weather reporting and other services, and air transport companies are 

 progressing in developing transport business. Fast and reliable com- 

 munication service has proved the backbone of weather and position 

 reporting and has been a valuable aid in the handling of traffic and 

 other matters relating to air transportation. Teletypewriter circuits 

 used for land service have been found particularly suited to meeting 

 the various requirements involving simultaneous communication with 

 many stations at remote distances. Other wire communication 

 services such as long distance telephone and commercial telegraph 

 have also aided, particularly in reaching points not served by tele- 

 typewriter circuits. It is expected wire communication service will 

 continue to be used extensively in connection with air transportation 

 and will be of considerable aid in its future development. 



Bibliography 



1. Airway Bulletin No. 1, September, 1931, issued by the U. S. Department of 



Commerce. 



2. Air Commerce Bul'etin March 1, 1932, issued by U. S. Department of Commerce. 



3. " Metallic Polar-Duplex Telegraph System for Long Small-Gauge Cables," by 



Bell, Shanck, and Branson, A. I. E. E. Trans., Vol. 44, 1925, p. 316. 

 " Voice Frequency Carrier Telegraph System for Cables," by Hamilton, Ny- 

 quist. Long, and Phelps, A. I. E.E. Trans., Vol. 44, 1925, p. 327. 



4. " Modern Practices in Private Wire Telegraph Service," by R. E. Pierce, 



A.I. E. E. Trans., Vol. 50, 1931, p. 426. 



5. " Police Teletypewriter Communication," by R. E. Pierce, presented at Great 



Lakes District Meeting, A. I. E. E., Milwaukee, Wis., March, 1932. 



6. " Printing Telegraph Systems," by John H. Bell, A. I. E. E. Trans., Vol. 39, Part 



2, 1920. 



7. " Air Transport Communication," by R. L. Jones and F. M. Ryan, A. I. E. E. 



Trans., Vol. 49, p. 187. 



8. " Aeronautical Communication," by E. Sibley, Jour. A. I. E E., p. 918, Novem- 



ber, 1930. 



9. " Airplane Flight Aided by Electricity," by C. F. Green, Electrical Engineering, 



August, 1931, p. 654. 



10. "Telephone Typewriters and Auxiliary Arrangements," by R. D. Parker, Bell 



Telephone Quarter, y, July, 1929. 



11. " Teletypewriter Service and Its Present Day Uses," by W. L. Dusenberry, Bell 



Telephone Qnarterly, April, 1931. 



I 



