I cannot judge by personal examination because when twelve hours later we ourselves arrived up at Danskeöen on board the “Fram” there was not a sign of fog to be seen. But I am inclined to believe that the fog has been composed of a layer of certain low-lying clouds, which had often been seen by us at the beginning of May while we were lying in Syd Gat waiting for suitable weather for the expedition’s start. These clouds will often just form suddenly when a cold wind blows from the polar ice towards the open sea. The moment the air arrives over the first water-lanes or open sea it gets heated from below. The heated layer rises above and whilst ascending forms clouds. Other colder parts of the air then come into contact with the water, get heated and rise also forming clouds, etc. According to the observations which we had occasion to make at Danskeöen in the beginning of May, the lower surface of these clouds is about 200 meters from the ground. Below this there is generally a thick mist of fine snow which reduces atmospheric visibility and will certainly be very disturbing for flying. Luckily these clouds do not reach to any great height, seldom over 1,000 meters, so that one can easily fly above them. Besides, one can count on their not forming further north than where one finds open water channels of fairly large dimensions. It is therefore not _too_ risky to undertake a flight above the cloud-belt towards clearer weather farther north. The polar flyers took this risk, and quite rightly too. After two hours’ flight from Danskeöen going northwards there were no clouds, and on the remainder of the flight there was nothing that obscured the view over the polar ice. The expedition has here made a meteorological reconnaissance of great importance to all later flying explorations in the Arctic. If a cold wind blows from the Pole one must reckon with the formation of a low cloud belt over the wider water channels, even if it is cloudless nearer the Pole. These clouds will form at all seasons of the year, but perhaps mostly in the colder periods, when the difference in temperature between ice and sea is greatest. The landing took place in a light wind, therefore probably near to the center of the high pressure region, which covers the Arctic Sea. On the way into the high pressure region the wind, however, must have been considerably stronger as is shown by the very considerable deviation of 250 kilometers on an eight hours’ flight. In the middle period of the flight it must therefore have been thirty kilometers per hour, which is considerably more than the pilot observations over King’s Bay had shown, namely, twenty kilometers per hour. The aeroplanes must have flown, therefore, through a zone with strong northeasterly winds blowing north of Spitzbergen, and then later come into calmer wind conditions nearer the Pole.