Abstract
THE formula giving the variation of the earth‘s horizontal field with depth quoted in the letter of Hales and Gough involves an approximation concerning densities which is only applicable to spheres the density distribution of which is only slightly different from a uniform one, such as is roughly true for the earth. Thus it is not to be expected that the formula should give the dipole variation law when ρ 1 = 0, but I am grateful to Prof. Chapman for pointing out a more general formula. It should be noted, however, that in the present state of the theory of Blackett‘s formula, , the treatment of densities must remain ambiguous, various assumptions leading to slightly different values of the predicted variation with depth. This point will be dealt with in detail elsewhere.
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RUNCORN, S. Variation of Geomagnetic Intensity with Depth. Nature 161, 52 (1948). https://doi.org/10.1038/161052b0
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DOI: https://doi.org/10.1038/161052b0
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