1907.] on Recent Contributions to Electric IVave Telegraphy. G91 



be obtained. In 1908 Mr. Poulsen introduced a further improvement. 

 He found that by enclosing the arc in a vessel containing hydrogen 

 or coal gas, and forming the arc between a cold metal terminal, which 

 is the positive, and a large carbon terminal, which is the negative, the 

 arc being also traversed by a strong magnetic field, much higher 

 oscillation frequencies could be obtained than with the double carbon 

 arc in air (see Fig. 11). 



He also found it is an advantage to rotate the carbon terminal. 

 When this arc is shunted by an appropriate small condenser in series 

 with an inductance, we can obtain in this last circuit electric oscilla- 

 tions having a frequency of a ^million or more depending on the 

 capacity and inductance used. If a suitably tuned antenna is 

 connected to one terminal of this^condenser, and one arc terminal to 



Fig. 11. 

 Poulsen's Apparatus for Creating Undamped Oscillations. 



the earth, as shown in the diagram, we are able to radiate from the 

 antenna undamped trains of electric waves. 



I have before me an apparatus of this kind with which much 

 work has been done in my laboratory during the last few months. 

 It consists of a water- jacketed brass cylinder with marble ends, 

 through which project at one end a thick carbon rod, kept in 

 rotation by a motor, and at the other a water-cooled brass tube with 

 copper beak at the end. An electric arc is formed with 400-500 

 volts between these terminals taking 6-10 amperes. 



The terminals are connected by a sliding inductance and by a 

 condenser. Then, in addition, a long helix of wire is connected 



2x2 



