National Geographic : 1900 Feb
68 PRACTICAL EXERCISES IN GEOGRAPHY star circles remains fixed wherever the observer goes and however much his horizon changes from the position that it had at the pole. As the observer moves along any meridian toward the equator his horizon must progressively tilt from the position that it had at the pole; and the amount of tilting may be measured by the angle be tween the tilted horizon and any one of the star or sun circles. This is, in essence, the method of Eudoxus, already referred to. A third way from pole to equator the angle would be 30°; half way, 45°; two-thirds way, 600; at the equator, 90°. The rotation of the earth is thus of great assistance in determining the relative positions of places. Bearing these principles in mind, let the sun-circle be de termined and represented by a series of stakes in a school yard, as in figure 1. Stand about 30 feet to one side of the stakes, in such a posi PE . ''r--- . ^ NA FIGURE 1 tion that the tops of all of them fall into a slanting, straight line when the observer's head is lowered to the height of the highest stake; estimate or measure the angle, CAD, by which the horizon is de pressed beneath this slanting line*; and as the angle thus deter mined is to 900, so is the distance from the pole (measured along a meridian from the pole to the observer) to the entire quadrant of the meridian from pole to equator. Latitude is counted from the equator toward the pole; it will therefore be the complement of the angle just measured. It should be noted that latitude may be thus de termined at any time of year and without knowledge of the sun's angular distance from the sky equator (declination). * The pivot does not lie in the plane of the sun-circle, and the slanting line does not measure the sun's noon altitude, except at the equinoxes. The noon altitude of the sun varies through the year, but the slanting line (the slant of the plane of the sun-circle) is constant through the year, whatever the declination of the sun. In all this method of determining latitude it is assumed that the motion of the sun in declination in a single day will not be detected by the rough methods of record here employed.