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 diagrammatically 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 6 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 OC’ 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 
Fig. 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 
