C. W. Heaps

C. W. Heaps is the author of "The Hall Effect in Bismuth with Small Magnetic Fields" (Physical Review 29:332, February 1927; DOI 10.1103/PhysRev.29.332), the principal scientific rebuttal to Palmer H. Craig's reported anomalous low-field Hall coefficient.

Measurement

Heaps measured a bismuth plate of 0.011 × 0.9 × 2.0 cm over 0.07–2.40 gauss. He obtained an average R of 11.5, with variations with field smaller than experimental error — against Craig's reported factor-of-ten rise at the lowest fields. At larger fields Heaps found R falling from 13.5 at 650 gauss to 5.9 at 8600 gauss.

Experimental parameters reported: primary current 1.3 A; each R value the average of at least five readings; galvanometer 16.6 ohms at 17.3 mm per microvolt; reversing the plate to reverse the earth's field gave a 24 mm deflection. The bismuth was supplied as c.p. by Eimer and Amend.

Plate fabrication

Heaps prepared thin bismuth plates by molten-drop casting: a vertically clamped glass tube holding a bismuth rod, with a clean horizontal glass plate about 10 cm below, heated until a single large drop falls and spreads into a thin uniform circular film.

Critique of Craig's method

Heaps concluded that Craig's data were erroneous, probably from insulation leakage or uncompensated thermomagnetic effects. His methodological points:

• Craig grounded his potentiometer to increase stability, which Heaps reads as evidence of variable-resistance leaks.
• Craig did not report reversing the magnetic field to average out thermal effects.
• Craig measured Thomson and allied potentials only at the instant the longitudinal current was broken, and did not test the field's effect on them.

The recommended control is to reverse the magnetic field and average, since the Hall emf reverses with the field while thermal effects do not.

See also

Anomalous Low-Field Hall Coefficient in Bismuth, comparisons/comparison-craig-hall-effect-claims-vs-evidence.