In the night the icebergs are readily distinguished even at a distance by their natural effulgence, and in foggy weather by a peculiar blackness in the atmosphere. As they are not unfrequently drifted by the Greenland stream considerably to the south of Newfoundland, sometimes even as far as the fortieth or thirty-ninth degree of latitude (May, 1841, June, 1842), ships sailing through the north-western Atlantic require to be always on their guard against them. The ill-fated “President,” one of our first ocean-steamers, which was lost on its way to New York, without leaving a trace behind, is supposed to have been sunk by a collision with an iceberg, and no doubt many a gallant bark has either foundered in the night, or been hurled by the storm against these floating rocks. But though often dangerous neighbors, the bergs occasionally prove useful auxiliaries to the mariner. From their greater bulk lying below the water-line, they are either drifted along by the under-current against the wind, or, from their vast dimensions, are not perceptibly influenced even by the strongest gale, but, on the contrary, have the appearance of moving to windward, because every other kind of ice is drifted rapidly past them. Thus in strong adverse winds, their broad masses, fronting the storm like bulwarks, not seldom afford protection to ships mooring under their lee. Anchoring to a berg is, however, not always unattended with danger, particularly when the summer is far advanced, or in a lower latitude, as all ice becomes exceedingly fragile when acted on by the sun or by a temperate atmosphere. The blow of an axe then sometimes suffices to rend an iceberg asunder, and to bury the careless seaman beneath its ruins, or to hurl him into the yawning chasm. [Illustration: 30. SCALING AN ICEBERG.] Thus Scoresby relates the adventure of two sailors who were attempting to fix an anchor to a berg. They began to hew a hole into the ice, but scarcely had the first blow been struck, when suddenly the immense mass split from top to bottom and fell asunder, the two halves falling in contrary directions with a prodigious crash. One of the sailors, who was possessed of great presence of mind, immediately scaled the huge fragment on which he was standing, and remained rocking to and fro on its summit until its equilibrium was restored; but his companion, falling between the masses, would most likely have been crushed to pieces if the current caused by their motion had not swept him within reach of the boat that was waiting for them. Frequently large pieces detach themselves spontaneously from an iceberg and fall into the sea with a tremendous noise. When this circumstance, called “calving,” takes place, the iceberg loses its equilibrium, sometimes turns on one side, and is occasionally inverted.