1907.] on Rficent Contributions to Electric Wave Telegraphy. 701 



galvanometer used by me connected between the middle plate and 

 the negative terminal. As Mr. Marconi had before that time used 

 my oscillation valve with a telephone with it for long distance work, 

 and M. Tissot has found a galvanometer, used as I described it, 

 effective up to 50 kilometres, the modification made by Dr. de Forest 

 does not make any fundamental difference in the operation of the 

 device as a wave detector.* 



Very closely connected with the question of the production of con- 

 tinuous or undamped electric waves is that of the electrical trans- 

 mission of speech through space without wires ; in other words, 

 wireless telephony. Some considerable progress has already been 

 made in this direction. Any complete treatment would require a 

 lecture in itself. If, however, we pass by the investigations of Bell 

 with the photophone, Simon, Ruhmer, and others with apparatus 

 employing the resistance variation of selenium by projected beams of 

 powerful light, and also those of Preece, Gavey, and others with 

 electro-magnetic induction, we may say that at the present time the 

 chief interest attaches to methods of wireless telephony which 

 involve the use of undamped electric waves. The problem may 

 then be stated to be as follows : Articulate speech made against a 

 diaphragm at a transmitting station has to affect similarly the 

 diaphragm of a telephone at a receiving station not connected with 

 it by wire. 



Time only permits me to give you a brief sketch of some 

 interesting experiments which have been carried out lately by the 

 German Wireless Telegraph Company between Berhn and their large 

 station at Nauen, 20 miles distant. At the transmitting station they 

 employ 12 electric arcs in series, each of which is composed of a 

 carbon negative, and a water-cooled copper positive electrode. These 

 arcs take 4 amperes at -l-lo volts (see Fig. 14). In parallel with this 

 series of arcs is joined a condenser and inductance, to which is induc- 

 tively but loosely coupled an antenna from which undamped electric 

 waves, <S00 metres in wave length, are radiated, having a frequency 

 therefore of 400,000. The oscillations set up in this antenna can be 

 more or less enfeebled by shunting them to earth through a micro- 

 phone transmitter, the resistance of which is varied by the act of 

 speaking against it. Hence, although the wave length of the emitted 

 electric waves is not altered, their intensity is modulated in accordance 

 with the wave form of the sounds impressed on the transmitter dia- 

 phragm. At the receiving station there is a receiving antenna tuned 

 to the wave length used, having a quantitative electrolytic detector 

 in connection with a telephone coupled inductively to the antenna 

 circuit. Hence the vibrations of the transmitter diaphragm vary the 

 intensity of the radiated electric waves but not their wave length. 



* In a private letter M. C. Tissot has already acknowledged gracefully my 

 priority of invention in this matter, although he himself was independently 

 working in the same direction. 



