260 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



earlier work of Fessenden in this fascinating field, in which he was 

 pioneer. The wireless telephone speech was free from all disturbing 

 noises and interferences so common on ordinary telephone lines. 

 Briefly, such telephony depends on the abilit}^ to control the voice 

 waves and vary in accordance therewith the energy given out by the 

 transmitting antenna and to do this with a fairly large output of 

 energy. 



By employing a method I described about 1892, it is possible to 

 generate a continuous wave train by shunting a direct current arc 

 with a capacity (condenser) in series with an inductance, the fre- 

 quency rate depending on the electrical constants of these parts of 

 the apparatus. This system, which was the subject of the United 

 States patent taken out by me in the early nineties, has been vari- 

 ously called the Duddell singing arc, or later the Poulsen arc. Poul- 

 sen employed it with modifications in his system of wireless tel- 

 ephony. Long before this work of Poulsen, Fessenden had used a 

 high-frequenc}^ dynamo for securing the continuous train needed. 

 A suitable microphone transmitter was made to so alter the rela- 

 tions of the waves in transmitting and receiving antennae, that voice 

 waves could be received in an ordinary telephone connected with the 

 receiving antenna sj^stem. 



Much progress has been made in this department of wireless work, 

 and such telephony between Europe and America nuiy yet become 

 practicable. Methods are being worked out whereby it may be 

 possible to mold outputs of many kilowatts of energy so as to have 

 them vary with the voice waves, and when this is done many prob- 

 lems, the solution of which now seems remote, may become solved 

 and the results prove of great practical value. It was not, however, 

 my intention to devote time to these later researches, but to endeavor 

 to present to the mind's eye a view of the nature of wireless trans- 

 mission which should show the similarities to ordinar}^ transmission 

 by wire and also the differences. Furthermore, I hope I have shown 

 it to be evident that future transmission of energy at high efficiencies 

 will still demand the wire core for guiding that energy to its 

 destination. 



