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Comparison between measurements on spheres and cylinders shows that a short cylinder with axial ratio (length/diameter) ≃0.9 and susceptibility ≃0.8 (cgs) has an effective demagnetizing factor N ≃ 3.7 both in the axial and radial directions. Hence, for a short cylinder with high susceptibility, the sum of the effective demagnetizing factors in three mutually perpendicular directions is less than 4π. This is important to know e.g., when determining the magnetic properties of highly magnetic magnetite ore samples.

There appear to be some mistakes in the subject paper. The authors seem not to have realized that the anti‐symmetric contact anomaly represents one of the flanks of a symmetrical dike anomaly of infinite width, and that the symmetric contact anomaly belongs to the family of anti‐symmetric dike anomalies. This explains the peculiar looking curve for contacts (R = ∞ curve) in their Figure 2 where the contact curve is seen to intersect the dike curves. To be correct the R = ∞ curve has to be turned around a vertical axis so that the value for θ = 90 ends up at θ = 0 and vice versa. It may have added to the authors’ confusion that they used two different sources for the mathematical expression of contact and dike anomalies without realizing that the angle θ has different definitions in the papers cited. In the formulas given by Åm (1972) the angle θ has a value of 90 degrees for the symmetric and 0 degrees for the antisymmetric dike anomaly, whereas in Gay (1963) the angle θ has a value of 0 degrees for the symmetric and —90 degrees for the antisymmetric case.

We fully agree with James Clerk Maxwell and Sven‐Erik Hjelt that long rods should be used if one wishes to measure accurately susceptibilities, because this will eliminate the effect of demagnetization. However, this holds only if the material under measurement is homogeneous with one and the same susceptibility throughout. If the sample is not homogeneous, the magnetization will be inhomogeneous, and we are back to where we started.