Science for beginners . Fig. 168.—Measuring the boards shadow on December 22, at latitude 40°, North. 22i. How the Suns Heating Power Changes with Sea-sons and Latitude.—Since, at latitude 40°, the highest alti-tude of the sun is 73%° and its lowest altitude is 26%°, itis easy to show the area of the earths surface over which 1sq. ft. of suns energy is distributed at the summer solsticeand at the winter solstice. In Fig. 169 the horizontal linerepresents the earths surface. Two parallel lines, 1 cen-timeter apart, and cutting the horizontal line at an angle of731/2°, are drawn to represent the
Science for beginners . Fig. 168.—Measuring the boards shadow on December 22, at latitude 40°, North. 22i. How the Suns Heating Power Changes with Sea-sons and Latitude.—Since, at latitude 40°, the highest alti-tude of the sun is 73%° and its lowest altitude is 26%°, itis easy to show the area of the earths surface over which 1sq. ft. of suns energy is distributed at the summer solsticeand at the winter solstice. In Fig. 169 the horizontal linerepresents the earths surface. Two parallel lines, 1 cen-timeter apart, and cutting the horizontal line at an angle of731/2°, are drawn to represent the suns rays June 21 and thetwo parallel lines also 1 centimeter apart, but cutting the hori- 212 THE SEASONS—CLIMATE AND HEALTH. zontal line at an angle of 26%° represent the suns raysDecember 22. It is evident from this figure that the sq. suns rays is spread over just about twice as large anamount of earths surface on December 22 as on June 21. It follows that the sun will heatthe earths surface but one-halfas much on December 22 as itwill on June 21. In a like manner Fig. 170shows how the area of earthssurface upon which 1 sq. ft. ofsuns energy falls varies at lati-tude 49°, the north boundaryline of the United States. OnJune 21, the altitude of the sun at noon at 49° north latitudeis 64y2°; on December 22, it is but 17%°. In Fig. 170 thetwo parallel lines are therefore drawn at angles of 64%°and 17y2° to the horizontal. By measuring the distancesbetween the two pairs of parallel lines it is seen that the 1sq. ft, of suns energy is spread over about three times asmuch of the earths surface on December 22 as on June 21. Fig. 169.—Slant of sunsrays at 40° latitude, June 21and December 22. KALEV
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