Abstract
IN a recent letter1, A. L. Hales and D. I. Gough compared their measurements of Hd, the horizontal magnetic intensity (H) at depth d, made in the Witwatersrand at d = 4,800 ft., with the formula Hd/H0 = 1 - 2 (5Ï1/Ïp + 1) d/a (1) obtained by S. K. Runcorn from Blackett‘s theory2. In (1), Ho denotes the value of H at the overlying point on the surface (d = 0), a denotes the earth‘s radius, Ï1the mean density of the rocks down to depth d, and Ï the overall mean density of the earth. The observations were compared also with the formula Hd/H0 = a3/(a-d)3 = 1 + 3d/a (approximately), (2) corresponding to any âcoreâ theory which places the source of the field wholly below the depth d.
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References
Hales, A. L., and Gough, D. I., Nature, 160, 746 (1947).
Blackett, P. M. S., Nature, 159, 658 (1947).
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CHAPMAN, S. Variation of Geomagnetic Intensity with Depth. Nature 161, 52 (1948). https://doi.org/10.1038/161052a0
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DOI: https://doi.org/10.1038/161052a0
