150 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



cuit was superimposed an equipment for transmitting in one direction 

 telegraphic messages by means of sustained high-frequency oscilla- 

 tions, employing the telephone as the means for receiving the signals. 

 The circuit used is shown diagrammatiealry in figure 8, in which, in 

 the Morse set, there are shown between the line wire and the ground G, 

 the line relay S, the key K, and the line battery B; and the local 

 battery h and the sounder s; and in which, in the high-frequency 

 set, are similarly shown between the line wire and the ground G the 

 tuning elements C and L; and at the transmitting end the oscillation 

 transformer T, the primary of which is in circuit with the dynamo 

 as a source of sustained oscillations, the telegraph key K', the inter- 

 rupter I and the tuning elements C and L', and at the receiving end 

 the oscillation transformer R in the secondary circuit of which are 

 included the usual tuning elements and operatively connected to 

 them the detector and its telephone as a means of receiving the 

 signals. 



As noted in the case of the preliminary local circuit tests, it was 

 found that over this particular line it was not necessary to use a 



Fro. 8. 



detector for electromagnetic waves, since enough energy was delivered 

 to operate the telephone receiver by connecting it directly between 

 the line and the earth. 



The sound produced, however, was characteristically different 

 in the two cases. With the detector the individual signals had the 

 characteristic tone corresponding to the interrupter at the trans- 

 mitting end of the line, whereas without the detector this tone was 

 entirely absent, and a general dull sound, due to the resultant action 

 of the wave-trains was heard. If, however, a telephone receiver was 

 employed with a soft iron core, instead of a permanent magnet, no 

 result was obtained with the limited power used on this line. 



Although little mention of telegraphy by high-frequency electric 

 waves has been made thus far, as a matter of fact it was found 

 convenient during the experiments upon telephony actually to 



