ALTERNATING-CURRENT PLANEVECTOR POTENTI- 

 OMETER MEASUREMENTS AT TELEPHONIC 

 FREQUENCIES. 



By a. E. KENNELLY and EDY VELANDER. 

 (Read April 26, 1919.) 



History of the Apparatus. 



The measurements presented in this paper have been made in the 

 electrical engineering laboratories of the Massachusetts Institute of 

 Technology, with a new form of a.— c. planevector potentiometer, 

 giving its potential readings in rectangular coordinates. This in- 

 trument lends itself readily to the measurement of vector potential 

 differences up to frequencies of at least 2,000^-'. The principle of 

 the potentiometer is the same as that described by Professor Larsen^ 

 in 1910; but the present form of the instrument has been worked 

 out in the M. I. T. laboratories, mainly through the thesis studies of 

 Mr. A. E. Hanson.2 



The essential connections of the instrument and its method of 

 application are outlined in Fig. i. The anti-inductive resistance ah 

 is connected in series with the primary winding he, of a toroidal non- 

 ferric induction coil included in the main potentiometer circuit P. 

 The secondary winding hd, of the induction coil, is connected at h 

 with the junction of the primary coil and the resistance. The sec- 

 ondary winding of the induction coil, and the resistance ah, are both 

 provided with suitable taps, which are brought out to dials, for ad- 

 justment of the potential connections at k and /. When a sinusoidal 

 alternating current Ip r.m.s. amperes Z , from the oscillator source 

 O, at a suitable impressed frequency, passes through the potentiom- 

 eter circuit, the alternating p.d. between the taps k and / will be 



Ep=Ip(R-^jX), r.m.s. volts Z (i) 



where R is the resistance included between k and h in ohms, while 



1 Bibliography 9. 



2 Bibliography 13. 



PROC. AMER. PHIL. SOC. VOL. LVIII, G, JULY 22, I919. 



97 



