Von Middendorf collected statistics of the passage of birds in the Russian Empire, and by reckoning the average date of arrival of a few species at certain points of observation, worked out a number of curves or lines which he calls "isepipteses," or lines of simultaneous arrival (35). The result was, according to his argument, a general convergence northwards; the birds passing through Central Siberia travelled roughly in spring from south to north, in Eastern Siberia from south-east to north-west, and in Europe from south-west to north-east; they converged, in fact, upon the Taimyr Peninsula. This to some extent is doubtless true, but Middendorf goes on to prove that the magnetic pole is situated in this Peninsula and that the birds are drawn thither by magnetic influence, "in spite of wind, weather, night or cloud." He calls them "sailors of the air," possessed of an internal magnetic influence. He supports his argument by the statement that there is a similar convergence in North America towards the magnetic pole of the western hemisphere. But all birds do not go in the direction of the magnetic poles, and many of those which do, stop short at suitable breeding places long before they have travelled so far north. The Taimyr Peninsula, a vast area in the extreme north of Siberia, is each spring a "zoological vacuum"; towards this desirable spot migrants will stream. Herr Otto Herman cleverly shows the absurdity of many of the reputed routes by cartography; his map is crossed in all directions by the routes upheld by various theorists. Birds could not possibly follow all the directions "which authors invented for them," most of which he adds are founded on mere supposition (31). Dr Palmén, he shows, usually managed to avoid districts where there were no observers, but Mr Dixon and M. Quinet made their routes follow rivers and coast lines, whether there was evidence to support this idea or not.