austral auroras were frequent, but not remarkably vivid. One single drape-like aurora was seen; the others looked like luminous clouds traversed by moving rays. Insolation during the summer months is considerable. On the 30th of December the thermometer with a black ball marked +41°, while the temperature of the air was at -1°. The effect of that insolation is, however, but little felt upon the ice-pack; the upper layer of snow hardly melts in summer. ICE The observations made with regard to this subject confirm what was already known from the examination of the arctic ice. The ice directly produced by the freezing of sea-water is never of great thickness, but this thickness increases on one side by the accumulation of snows on its surface, and on the other by the heaping of blocks during the pressure. These mechanical phenomena are able to form slabs eight metres in height. The pressures are produced, in the regions explored by the _Belgica_, by the wind, which is thus foretold: In summer, during calm weather, there is always a change in the ice-pack, which is accompanied by a formation of cracks and leads. The pressure is produced afterwards, but before the wind is felt; it generally ceases some time after the wind prevails and when the ice-pack is drifting. This seems to me to prove that the pressure is the result of difference in the velocity of the drifting parts of the ice-pack, and this difference is due to the fact that a wind which begins to blow drives the portion of the ice-pack on which it blows upon the rest, which has not hitherto felt its influence. It must be said that the pressure may also be produced when the ice-pack is driven by the wind against land. The icebergs met by the expedition are incontestably formed by an ice which has a different origin from that which forms the ice-pack, properly speaking. An iceberg is indisputably a fragment of a terrestrial glacier. All the particulars which we have been able to state, concerning the structure of the floating iceberg, were equally observed in the structure of the façades of the glaciers of Belgica Strait. OCEANOGRAPHY