Over all the top of the world rested unbroken darkness like a cap. Through that polar night the flow of heat off into outer space was like the steady drain of blood from an open wound. As the air thus grew colder and colder, it shrank toward the surface of the earth, and to fill its place more air flowed in at the upper levels. Upon every square mile of snow-covered land and frozen sea thus rested hourly a heavier weight of air.

Until two days previous this accumulation had been relieved by a great flow of cold air southward from Siberia into China. But since that time a series of storms had developed, and by their interlocked winds had blocked off this flow. All China now had mild temperature.

If the earth had not been revolving, if it had presented no contrast of sea and land, or even if there had been no mountains, the frigid air might merely have moved out in all directions from the pole, pushing beneath the warmer air in somewhat orderly fashion, as ink spilled upon a blotter seeps out to form an ever larger circle. But actually the cordon of storms surrounded the polar air, holding it back by the force of their winds as a line of police, now jostled back a little, now pushing forward, restrains an angry crowd. In Greenland, in Alaska, and in Scandinavia, high mountains also were barriers. But elsewhere, here and there, the line of the polar front bulged southward, as the crowd pushes forward against the police-line, not everywhere, but at spots where those who are boldest or angriest, most wronged or most desperate, whisper to one another and make ready for the sudden push.

Or, as a momentarily defeated army driven within a fortress daily restoring its morale and knowing itself too strong for the besiegers begins to renew the battle, so the polar air pushed out southward, now here, now there, feeling for weaknesses. Blocked in China, it thrust down the open ocean-corridor between Norway and Greenland; but a wide-spreading storm moving swiftly out from New England across the Gulf of St. Lawrence brought rain and snow to the mid-Atlantic and checked that sally. So the polar air pushed elsewhere, at every point where the mountain barrier was broken or the storms seemed weaker—into the broad arctic plain of Canada, at Bering Strait, under the lee of the Ural Mountains.

•