Статья. Опубликована в Physical Review, 1922, vol. 19, No 5, p. 456-466
Piezo-electric Method of Measuring Extremely Small Magnetostriction Effects. In this method, suggested by Pupin, the wire to be studied is surrounded by a solenoid through which an alternating current of known strength and frequency is sent, and the vibrations set up in the wire are transmitted to a piezo-electric crystal and the resulting electric charge is amplified and measured. (1) For elongations down to 2 X 10^-9 the wire was hung directly from a quartz crystal. To measure the charge produced by a given magnetizing current, an electromotive force of the same frequency and adjusted by means of a Pupin wave balance to the proper phase, was fed to the amplifier through a vacuum tube in parallel with the one connected to the crystal, and the potential was varied until the note produced by the crystal was balanced out. The force corresponding to a given charge was determined with the aid of a condenser, one plate of which was suspended from the crystal. (2) By using the torsion of a Rochelle salt crystal, the sensitiveness was extended to 2 X 10^-11 and (3) by tuning both the crystal and the wire to resonance with the frequency used, a sensitiveness of 3 X 10^-12 was reached. The last two arrangements were calibrated in absolute units by comparison of the results with those obtained with quartz. The smallest change previously measured was about 10^-8.
Magnetostriction with Small Magnetizing Fields. An iron wire containing 0.1 per cent. C, and a wire of electrolytic nickel were studied. In each case the curve for magnetostriction as a function of the field is nearly linear, but slightly concave downward, and apparently passes through the origin. For fields of 1, 0.05 and 0.002 gauss, the ratio of magnetostriction to field strength is respectively 3, 2.4 and 4 X 10^-9 for iron, and 2, 1 and 3 X 10^-9 for nickel. The probable error is from 7 to 10 per cent. The effect of increasing the tension is to decrease the elongation of both metals. A rod of bismuth 8 cm. long was tested in a field of 12 gauss using the resonance method, but gave a negative result, indicating that the effect is at least 10,000 times less than for iron.
Pupin Wave Balance for varying the Phase of an Alternating Electromotive Force is described.
