194 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
to ninety-five cycles the power-factor decreases, reaching a min- 
imum again and thereafter increasing rapidly. The broken 
curves’ of current and power-factor, figure 24 (d) and (e), are 
computed from the impedance diagram and their wide diver- 
gence from the curves showing the actual conditions is un- 
doubtedly evidence, not of the inaccuracy of the experimental 
and theoretical work, but of the disturbing effect of higher 
harmonics in the voltage wave. 
A consideration of both the observed and computed results 
led to the conclusion that it would be well to make the re- 
sistances of the two branches of the parallel circuit practically 
equal and to equalize the reactances of both the parallel and 
series circuits for sixty cycles, this frequency being mid-way 
(in effect upon reactance) between thirty and 120 cycles, the 
limits of the generator. It was also thought best to reduce the 
reactances of the parallel circuit and to increase those of the 
series circuit. After a few trials the circuit of Plate X (e) 
was built up with very satisfactory results which will be dis- 
cussed in some detail. In order that higher harmonics might 
be eliminated as far as possible a coil of seventy ohms reactance 
(sixty cycles) was inserted in series with the circuit to be 
studied. This served its purpose very well as is indicated in 
Plate X (d) in which the computed current and observed cur- 
rent do not differ materially. 
Plate X (a) is a polar diagram of the impedances of the 
parallel circuit. The symmetry of the figure should be noted, 
the result of balancing the susceptances at sixty cycles and 
working over a range of thirty to 120 cycles. Plate X '(b) is 
a similar diagram for the series portion of the circuit. These 
two diagrams bring out in a very striking way the difference in 
the characteristics of the two circuits. The phase relations are 
just opposite, as is also the manner in which the magnitude of 
the impedance changes with variation in the frequency. By ad- 
ding the impedances of the two circuits, frequency by frequency, 
Plate X (c) is obtained. At extreme frequencies the effect of 
the series circuit predominates. Near sixty cycles the effect 
of the parallel branch becomes more important and as a result 
the total impedance passes through two minima and one maxi- 
mum. The total impedance hodograph winds up on itself and 
takes on a form very much like that of a strophoid. This dia- 
