150 WILLIAM M. BARRET 
coil, the balance is disturbed because the inductance of the test coil has 
changed. The balance is restored by altering the inductance of a variable in- 
ductor placed in the arm with the test coil. When this operation is completed, 
the reading of the inductor dial indicates, by means of a calibration curve, the 
susceptibility of the sample. These variations in inductance are frequently so 
very slight that the effect must be amplified by vacuum-tubes, and even then 
only the most sensitive galvanometers will prove suitable. 
ELECTRIC CIRCUITS 
The electric circuits of the Susceptimeter are shown in Fig. 2. The ratio 
arms, R,; and Rs», consist of equal pure resistances, while one inductive arm in- 
cludes the test coil ZL; and variable inductor L2, and the other contains the 

nes on ae a Rg 
Meh 
ay 
Tie. 
4 
iG 
Me 

ee 
Fig. 1. Susceptimeter arranged for use with external vibration galvanometer. Several 
sample containers, filled with pulverized materials, may be seen near the galvanometer. These 
glass containers are provided with aluminum friction caps, and have outside dimensions of 2.7 
cm dia. by 10 cm long. 
tapped inductance L3, and vernier variable inductor Ly. The resistance bal- 
ance of the bridge is accomplished by means of 75, and this balance is main- 
tained for different positions of the inductance switch, S,, by the loading re- 
sistors 7; and fe. : 
Low potential alternating current is supplied the bridge through the 
transformer 7. The selector switch, S,, and variable resistor, 74, provide 
means for adjusting the bridge current, while its value may be determined 
with the ammeter A. a 
18 
