THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 

 JOURNAL OF SCIENCE. 



c s r -J[SIXTII SERIES.] 

 AUGUST 1921. 



XXV. O/i £fo Form of Free Triode Vibrations. By E. V. 

 Appleton, M.A.\ M.Sc, Assistant Demonstrator in Ex- 

 perimental Physics, University of Cambridge, and Balth. 

 van der Pol, Jiinr., D.Sc, Conservator Physical Labora- 

 tory of Teylers Institute, Haarlem (Holland) *. 



D 



[Plates VIII., IX., & X.] 



URING the last few years the triode vacuum-tube 

 generator has become the standard low power source 

 of alternating current for laboratory purposes. In an oscil- 

 lographic study of such a generator of acoustic frequency 

 designed for bridge measurements-, it was thought in- 

 teresting to obtain records of the temporal variations of the 

 currents in the subsidiary as well as in the output circuits of 

 the generator. The simplest type of self-excited oscillator 

 circuit was used (see fig. 1), the current-time records being- 

 obtained with a Duddell Oscillograph. 



Fig. a, PI. VIII., illustrates the current changes through 

 the coil Lj which forms part of the oscillatory circuit; it is 

 of no particular interest other than to illustrate the sinusoidal 

 character of the current in the output circuit and to show 

 the extreme steadiness of the generator. The temporal varia- 

 tions of the anode current flowing through the tube for two 

 oscillation frequencies of 450 and 660 per second are shown 

 in figs, b and c (PI. VIII.). These are of interest because oi 



* Communicated by Professor Sir J. J. Thomson, O.M., F.R.S. 

 Phil. May. S. 6. Vol. 42. No. 248. Aug, 1921. P 



