THERE are few civilizations set in such a varied yearly climatic cycle as is the Koyukuk. The difference between the short, sunless, snow-filled days of December, and the verdant, twenty-four-hour days of June and July, is almost the difference between two worlds. All the economic activities of the people, all the social habits, even the psychological reactions are revolutionized by the passage of the seasons.
Viewed from a scientific standpoint, the basic force behind all these differences is the fact that the earth's axis is tilted at an angle of 23° 27′ away from a perpendicular to its orbit. This tilt, as we all learned in fourth grade geography, means that in summer the northern regions of the earth are pointed toward the sun, while in winter they are faced so much away that even at mid-day the sun in many places cannot clear the horizon. The Arctic Circle is an imaginary line the same number of degrees from the North Pole as the earth's axis is tilted. As one travels north from the Circle there is a constant increase in the number of sunless days of winter as well as the days of midnight sun in summer, unless local topography happens to alter theoretical conditions.
Of course, in any mountainous country local topography does. Thus at Wiseman, which is only one degree north of the Circle, there are thirty-one consecutive days, from De-