Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/56

32 is quite sufficient to prove the correctness of the idea illustrated in Fig. 6, it nevertheless might be asked whether the other results of geophysics are compatible with it.

It is obvious that the gravity measurements in the oceans will be satisfied by our assumption in at least as good a manner as by the earlier one, according to which the outermost skin of rock is thinner here, but is, however, not quite absent. For they only signify that the rock beneath the oceans is heavier than that under the continents. We need not go any further into this question.

From investigation in earth magnetism, to which A. Nippoldt drew my attention, the view is generally held that the floors of the oceans consist of more strongly magnetic, therefore probably more ferruginous, material than the continental blocks. This is especially emphasized in the discussion over Henry Wilde’s magnetic model of the earth. Wilde covered the oceanic areas with sheet-iron in order to obtain a distribution of magnetic force corresponding to the earth’s magnetism. A. W. Rücker described this attempt in the words: “Mr. Wilde has produced a good magnetic model of the globe by means of an arrangement which consisted in effect of a primary field due to a uniformly magnetized sphere, and a secondary field due to iron, placed near the surface and magnetized by induction. The principal part of the iron is placed under the oceans. … Mr. Wilde attaches the greatest importance to the covering of the oceans with iron.” Raclot has also recently confirmed the opinion that this attempt of Wilde represents very well in broad outlines