4-4 Dr. LtlcLachlan on Effective Inductance, Effective 



condenser reading is observed (Cx should be small, L large, 

 and the frequency fairly high) : also the reading of the 

 m ill iam meter. The magneto is then connected in parallel 

 with G l5 and the latter is varied until resonance is again 

 obtained. The difference in the condenser readings (the 

 condenser should have an open scale) is the self-capacity 

 of the coil. It was found that the self-capacity did not 

 vary much with the frequency (2 x 10 4 to 8 x 10 4 ~), but it 

 was less when the armature was out of the housing than 

 when it was in, as one would naturally expect. When the 

 armature was out of the housing, the iron core, which was 

 a little longer than the armature coil, made little difference 

 in the self-capacity. With the armature in the housing 

 and the primary winding not connected thereto, the self- 

 capacity Avas less than that with the primary connected 

 to the housing but greater than that out of the housing. 



Theory of method. — To simplify matters we shall assume 

 the secondary coil with parallel condenser to be approxi- 

 mately represented by an inductance L having resistance R 

 in parallel with a condenser C equal to the self-capacity 

 of the coil, plus the condenser in the secondary circuit. 

 Neglecting dielectric loss, the admittances of the two paths 

 between A and B are respectively (see fig. 5) 



^ ; — =— and jcoG. 



R 2 +jco L 2 



Fig. 5. — Equivalent (assumed) circuit of secondary coil for 

 determination of self- capacity. 



Ik 



I I Se/f Capacity + 

 Added Capacity 



The combined impedance between A and B is therefore 



1 



Z = 



- /CO (J 



}{ 2 -\-jcoL 

 R 2 +^o) L 2 



_ (R 2 +> L 2 ) ( A — /a) C R 2 ) 

 A 2 + eo 2 C 2 R 2 2 ' 



where A = {l-co 2 L 2 C) 

 (1 -co 2 L 2 (J) R 2 + co 2 L 2 (_'R 2 +>L 2 (1 - q)-L 2 0) -jco CR 2 2 

 o) 4 L, 2 C. 2 + o) 2 C 2 R, 2 



