MEASUREMENTS AT TELEPHONIC FREQUENCIES. Ill 



so that 



b = TTT = o I 7o "o = o mhos, (q) 



I 2- 1 r- + /-o)- r~ 



/oj + — 



Ice 



Consequently, at minimum admittance and maximum impedance, 



ceo = , mhos (lo) 



J,. 



/co + - 



10} 



or 



I 



c = s farads, (ii) 



'"'- + 1 



It may be noted that the condition of maximum-impedance in the 

 Ic combination, and which has been defined as " parallel resonance," 

 corresponding to zero total susceptance, differs from the condition 

 of simple series resonance within the Ic circuit, which occurs when 

 the total reactance is zero, or when 



CO) = J- mhos. (12) 



/co 



This condition is found in the diagram, Fig. ga, at the total vector 

 admittance os, when the capacitance in c is 1.332 /xf. This occurs 

 when the angle sol. Fig. 9, is 90°, or when the angle iiso is equal to 

 the angle nol of the coil's admittance. The angle sou is 6°. 7', the 

 complement of mo/. 



In Fig. gb, the impedance OS of the Ic combination is that which 

 is presented at series resonance. It has the value 2135 'v 6°. 7' 

 ohms. The angle SOU is the same as the angle sou. At the ca- 

 pacitance c= 1-317 /if-, the p.d. at qq', on the Ic combination, will 

 be in phase with the main current. 



If we increase the impedances of Fig. gb by the fixed impedance 

 in the remainder of the circuit, Fig. ya, we obtain the total circuit 

 impedance as shown in Fig. gc, where OM' is the vector impedance 

 126 — y447.3 = 464.7 \ 74°. 16'. If we add to this fixed impedance, 

 OM', the vector circle LUS of Fig. 9b, we obtain the resultant vec- 



