ALTERNATING-CURRENT SUSCEPTIBILITY METER 153 
bridge is excited with alternating current, and the galvanometer and ampli- 
fier connected in the indicator circuit. With no sample in the test coil Z;, and 
with the variable inductor Lz adjusted for maximum inductance (dial reading 
0), the vernier inductor L, is used to bring the galvanometer pointer to mid- 
scale position. 
If a specimen, having a susceptibility greater than air, be now introduced 
into the test coil, the galvanometer pointer will move toward the positive 
side of its scale, and to rebalance the bridge it will be necessary to reduce the 
inductance of L»2. This is accomplished through the aid of a micrometer drive 
mechanism, provided with a vernier dial, which makes it possible to adjust 
and read the position of the variable inductor to within 1/100 scale division. 
The proper decrease in Lz is obtained when the galvanometer beans again 
1600 
VOLUME SUSCEPTIBILITY x 10° IN C.G.S. UNITS 


nme fo Ed 
(2 (a oe a a es 
p24 a 
DIAL READING OF INDUCTOR A IN DEGREES 
Fig. 3. Normal calibration curve for first selector switch position. For second or third 
position, a constant additive correction is applied, its value depending on switch position used. 
assumes its equilibrium position. The dial reading of the variable inductor is 
then a measure of the susceptibility of the unknown sample, and by employ- 
ing a calibration curve similar to Fig. 3, the dial readings may be conveni- 
ently converted to susceptibility values. To extend the range of the instru- 
ment, the tapped inductance L3, and selector switch S; are used. When the 
second or third selector switch position is required, a constant additive cor- 
rection is applied to the normal calibration curve, the value of the correction 
depending on the switch position used. 
Should a diamagnetic specimen be inserted in the test coil, the galvanom- 
eter pointer moves in the direction of the negative part of its scale, and for 
this condition, the initial balance is obtained with the inductor Lz set at 
some arbitrary scale position, and then its inductance increased until the 
galvanometer again indicates a balance. The same calibration curve employed 
21 
