152 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



The same general statement can be made relative to any of the 

 standard forms of low-frequency telegraphy over wires as now 

 practiced, such as the polar duplex, the differential duplex, and the 

 duplex-diplex, employing alternating currents of low frequency and 

 standard keys, relays, and sounders. 



Inserting a regular 150-ohm telegraph relay in series in the line 

 cuts down the high-frequency current to a small percentage of its 

 original value, which indicates the marked influence of the presence 

 of iron in such a circuit. Furthermore, it was noted that at 100,000 

 cycles the hysteresis of the iron core was so great that it became 

 heated very perceptibly in a few moments. 



Since a portion of the telegraph lines now used is still composed 

 of iron wires, it would be expected that electric waves would be 

 propagated over such wires less efficiently than over copper wires, 

 although it is well known that electric waves penetrate only about 

 one-thirteenth as deeply into soft iron for a given frequency as into 

 copper, but this is modified by the fact that the iron in telegraph 

 wires is not soft iron and in addition is galvanized. 



[Section 4 of this paper, giving details of measurements of electric 

 waves of frequencies from 20,000 to 100,000 cycles per second on a 

 standard telephone cable line, is omitted from the present reprint 

 by the Smithsonian Institution.] 



SUMMARY. 



Radiotelegraphy has no competitor as a means of transmitting 

 intelligence between ships at sea and between ships and shore stations, 

 and on land it is also unique in its usefulness in reaching isolated 

 districts and otherwise inaccessible points. To what extent it may 

 be also developed to furnish practical intercommunication according 

 to the high standard now enjoyed in thickly populated districts it 

 is not attempted to predict. 



The foregoing experiments indicate that either the existing wire 

 system, or additional wires for the purpose may be utilized for the 

 efficient transmission of telephonic and telegraphic messages, and 

 the former without interfering with the existing telephone traffic on 

 these wires. 



The fact that each of the circuits created by the use of super- 

 imposed high-frequency methods is both a telephone and a telegraph 

 circuit interchangeably, makes it possible to offer to the public a new 

 type of service, which it is believed will offer many advantages to 

 the commercial world. This type of circuit should be particularly 

 applicable to press association service, railroad service, and leased 

 wire service of all lands. 



The experiments described should not be interpreted as in any way 

 indicating limitations to radio telegraphy and telephony in the future, 

 for their present rapid development gives justification for great pros- 



