It is well known that the earth's “permanent” magnetic field is a most complex one. Gauss was the first to show how to analyze this field mathematically without making any assumption with regard to the actual distribution of the magnetism within the earth's crust. For a first attempt, he found it sufficient to embrace in his analytical expression terms to the fourth order. With the exception of the first‐order terms, which represent a homogeneous magnetization about a diameter inclined to the earth's rotation axis by an angular amount of about 12°, no physical interpretation of the various terms has as yet been given.
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L. A. Bauer (1897) studied this question.