SJiort Continuous Electromagnetic Waves. 9& 



further that by varying the filament current, and conse- 

 quently the filament temperature, it is not only the amplitude 

 of the oscillations which is altered ; the increased sag of 

 the filament at 'higher temperatures obviously alters the 

 capacities between F-P and F-G. In fact a change of 

 wave-length up to 1*5 centimetre was observed with different 

 filament temperatures, the other parameters of the circuits 

 being kept constant. (See Table I.) 



Table I. 



Fil. current. Wave-length. 



0-920 A . 374-20 cm. 



0-965 A 375-04 cm. 



0-980 A 375-70 cm. 



The smallest continuous wave produced in this way was 

 3*65 metres. When the wave-length was increased by the 

 means described above, the amplitude could be made consi- 

 derably greater, and the amplitude of the 3*75 metre wave 

 was more than sufficient to work with. When finally the 

 input is defined as the product of mean plate current into 

 plate battery E.M.F., a convenient input giving ample 

 energy for a great variety of measurements is 1 watt. 



Resonator (fig. 2). 



As resonator it is convenient to use as Lecher wires two 

 horizontal parallel telescopic brass tubes about 4 centimetres 



Fis. 2. 



o 



E 



HI 



£_ 



apart, with the two ends nearest to the thermionic tube, say 

 50 centimetres from the latter, and supported by a glass 

 cross-tube on which the Lecher wires (tubes) can easily be 

 mounted with some sealing-wax. The other ends of the 

 telescopic tubes are fixed in a piece of ebonite with two 

 mercury cups connected to the two Lecher tubes respectively. 

 This latter support A is mounted on a wooden stand in such 



