Science for beginners . ocean and brings more air and higher pres-sure to the land. This higher pressure over the land ( and 166) crowds the bottom air outward toward theoceans, in winter. That gives prevailing northwesterly windsand much fair cold weather to our northern plains and upperMississippi Valley, during the winter months. Similar out-flowing winds occur on all continents in winter, except whereother conditions may interfere. CHAPTER IVTHE SEASONS—CLIMATE AND HEALTH I. THE SUN— THE CAUSE OF THE SEASONS 219. The Suns Altitude and Its Heating Effect.—The height of the sun above
Science for beginners . ocean and brings more air and higher pres-sure to the land. This higher pressure over the land ( and 166) crowds the bottom air outward toward theoceans, in winter. That gives prevailing northwesterly windsand much fair cold weather to our northern plains and upperMississippi Valley, during the winter months. Similar out-flowing winds occur on all continents in winter, except whereother conditions may interfere. CHAPTER IVTHE SEASONS—CLIMATE AND HEALTH I. THE SUN— THE CAUSE OF THE SEASONS 219. The Suns Altitude and Its Heating Effect.—The height of the sun above thehorizon at noon is different forevery different latitude uponany given day. It also is dif-ferent for any given latitudeupon different days of theyear. The earth receives ailits heat from the sun. Weshall soon see that the nearerthe sun is to being at thezenith (the point directly over-head), the greater is its heatingpower. Therefore, the chang-ing altitude of the sun is one of the principal causes of seasons. Fig. 167. Exercise 49.—To Construct a Clinometer and to Measure theAltitude of the Sun (a) On a piece of cardboard about 20 in. square, mark out thequarter of a circle as shown in Fig. 167. To do so, make a smallloop at the end of a piece of wrapping twine. Slip a pencil pointthrough this loop. Place one finger tightly upon the string so as tomake the radius exactly 20 in. Draw the arc of the circle from 0°to 90°. Next mark off the scale by dividing the distance from 0°to 90° into eighteen equal parts. Each space will then represent 5°.If the radius is exactly 20 in., the distance from 0° to 90° aroundthe arc is % of 2 X 20 X in., or in. Each of the eighteenequal parts will then be a trifle less than 1% in. These 5° spacesmay then easily be divided into five equal spaces, thus marking offdegrees. 209 210 THE SEASONS—CLIMATE AND HEALTH (b) Tack this cardboard scale to a board about 2 ft. a nail into the board at the center of t
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