Blocking the norther’s path, to the southwest lay the wall of the Mexican Cordillera; to the southeast, the highlands of Chiapas and Guatemala. But between were only the low hills of the Isthmus of Tehuantepec, and into that gap the wind poured as into a funnel. It spent the last of its rain upon the northern slope; dry and cool it started down toward the Pacific. Descending, it warmed; it ceased to be a chilling blast from the Arctic and became almost mild. But because of the funnel, the wind was stronger. On the Pacific it met the steamers from Panama, and buried them bows-under. “Tehuantepecker!” explained the stewards. “Have to expect them this time of year.” The captains logged a ten-point gale.

Grown moist again from the tropical ocean, the wind skirted the coast of bananas and coffee. Striking the mountains the air exploded in thunderstorms. “Chubasco!” said the Salvadoreans. Like the men farther north, the soft Nicaraguans shivered in a cold wave, although the temperature did not fall below fifty-six. “Papagayo!” said the Costa Ricans.

At last, having penetrated to within ten degrees of the Equator, grown warm in the tropical sun, the far-sent invasion from the north felt the drag of that great current of air which belts the earth’s central zone, and turning westward mingled with the steadily blowing trade wind.

4

Theoretically, the J. M. knew that such things could happen. At the Institute he had even heard a visiting specialist in dynamic meteorology read a paper on the synoptic preliminaries of a polar outbreak and demonstrate mathematically the sources of energy involved. Nevertheless, when he saw the map that morning, the J. M. almost gasped. To know that all this was in the actual process of happening was very different from thinking of it as equations—and at the same time to realize that as part of the Weather Bureau he carried his share of responsibility for charting it and forecasting its progress. He felt as if the government of the air had suddenly been overwhelmed by revolution.

In the orderly hemisphere of the text-books there was a high-pressure area over the Pole and another near the Tropic of Cancer in what were known as the “horse latitudes.” Between the two, in the temperate zone, a succession of storms moved steadily from west to east. South of the sub-tropical high pressure was low pressure again, and the trade winds blowing from northeast to southwest.

But now, in two great tongues of cold air, the polar high pressure had broken clear through the chain of storms. It had joined with the high pressure of the horse latitudes, and even broken into the region of the trade winds.