conversations with wegener, the author of continental drift theory, got milanković interested in the interior of the earth and the movement of the poles, so he told his friend that he would investigate polar wandering. in november 1929, milanković received an invitation from professor beno gutenberg of darmstadt to collaborate on a ten volume handbook on geophysics and to publish his views on the problem of the secular variations of the earth's rotational poles. wegener presented extensive empirical evidence in his scientific work on the 'great events' during the earth's past. however, one of the main findings that especially preoccupied wegener and then milankovitch was the discovery of big coal reserves on the svalbard islands, in the arctic ocean, which could not form at the present latitude of these islands. in the meantime, wegener died (from hypothermia or heart failure) in november 1930 during his fourth expedition to greenland. milanković became convinced that the continents 'float' on a somewhat fluid subsurface and that the positions of the continents with respect to the axis of rotation affect the centrifugal force of the rotation and can throw the axis off balance and force it to move. wegener's tragedy additionally motivated milankovich to persevere in solving the problem of polar wandering.