192 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
stants of the circuit so as to improve the results but they proved 
unsuccessful, showing that a careful analysis had to be made 
before any accurate prediction of the effect of changes in the 
circuit 'could be made. Some of this work has already been 
described. 
Although the current characteristics of the circuits gave the 
clue to the results to be expected it is, of course, as .impedances 
that the two circuits must be added. The impedance of the 
parallel portion (a) and the series portion (b) of the total 
circuit are plotted in figure. 24 (a) and (b). They are plotted 
vectorially and when added give figure 24 (a) + (b) which rep- 
resents the change in the total impedance with variation of 
frequency. From this figure the broken curves of figure 24 (d) 
and (e) are computed. 
If the total impedance hodograph is followed one will see 
that with increase of frequency (voltage constant) the corre- 
sponding current must increase slightly from thirty to thirty- 
five cycles and then decreases until sixty cycles is reached. It 
will then increase to a maximum at about ninety-five cycles 
and finally decrease. The power-factor increases rapidly to 
unity at forty cycles. Between forty and fifty-five cycles it is 
very nearly unity and the current is lagging. From fifty-five 
