Production of Sho?*t Electromagnetic Waves. 

 Vibrator (generator). 



91 



W. C. White has described * a method for generating 

 continuous waves o£ 6 metres by means of a three-electrode 

 thermionic tube. By using an ordinary hard small receiving; 

 " valve " and a similar circuit, I have found it possible to 

 obtain continuous waves of still higher frequency. The 

 connexions are as shown in fig. 1. Here P is the plate,. 



G the grid, and F the filament. The tuned plate circuit can 

 be considered to consist of the wire PBO, principally acting as 

 inductance, in series with the condenser C and the capacity 

 existing between filament and plate. The grid circuit, which 

 is also tuned, is formed by the wire GAF (which again 

 principally represents the inductance) in series with the 

 condenser formed by the filament and grid. The condenser 

 C is shunted by an accumulator battery B x in series with a 

 milliammeter, while the filament is heated by the battery B 2 , 

 the heating current being read on the ammeter A 2 . 



The necessary reaction from the plate circuit on the grid 

 circuit is hero obtained (instead of by the usual electromagnetic 

 coupling) by a capacity coupling inside the thermionic tube, 

 the grid being placed in the electric field between filament 

 and plate. It happens that this coupling has the proper sion 

 to maintain strong oscillations. 



In our experiments the valve was supported in a wooden 

 clamp over a piece of paraffin-wax with four mercury cups 

 in it. The four terminals of the valve were dipped in these 

 cups. The wires PBC and GAF were each about 60 cm. lono T 

 while the connexion CF was kept a few centimetres. The 

 variable condenser (J consists ot two vertical zinc, plates of 

 about 10 cm. diameter mounted on paraffin blocks in such a 

 May that their mutual distance could easily be varied by hand. 

 It is advisable to put a piece of paper or other insulating 

 material between the plates in order to prevent them from 

 touching, and short-circuiting the battery Bj. The length of 



* Gen. Electr. Review, p. 751 (1910). 



