282 THE SEASONS CLIMATE AND HEALTH 



(b) Tack this cardboard scale to a board about 2 ft. square. 

 Drive a nail into the board at the center of the circle. Bore a 

 hole in the board near its upper edge and in the center from right 

 to left. Hang this instrument on the east side of the house where 

 the sun can strike it at noon. 



NOTE. If the instrument is to hang on the west side of the house 

 make the scale by beginning with in the upper left-hand corner. 



(c) See that the clinometer hangs in a north and south line, and that 

 no trees or buildings prevent the sun's striking it at noon. At 12 

 o'clock one day each week, note where the shadow of the nail falls 

 across the scale. Read and record with date the angle made by the 

 nail's shadow with the line. This angle is equal to the angular 

 altitude of the sun above the horizon. Explain why. After making 

 several readings, state what you have discovered. 



308. Effect of the Sun's Altitude upon Its Heating Power. 



In all portions of the United States the sun's rays are much more 

 nearly vertical in summer than in winter. Throughout the 

 United States the sun is at its highest altitude and its rays are 

 most nearly vertical on June 21 ; it has its lowest altitude and 

 the rays are most slanting on December 22. The highest and 

 lowest altitude of the sun's rays vary with the latitude. At 

 latitude 40, which is about the latitude of Philadelphia, 

 Columbus, Ohio, Springfield, 111., and Denver, Colo., the high- 

 est altitude of the sun is 73J^ and the lowest, 



Exercise 64. To Measure the Length of Shadow when the Sun is at a 

 Known Altitude 



Place a table or desk having a level top before a south window. 

 Cut out a piece of cardboard just 1 ft. square. At 12 o'clock, noon, 

 on a clear day read the sun's altitude from the clinometer. Then 

 set the cardboard on edge in an east-and-west line on the table before 

 the window (Fig. 211). Lean the top of cardboard toward the north 

 till it exactly faces the sun. The cardboard will then form an angle 

 with the table top which equals 90 minus the altitude of the sun. 

 Its shadow now falls upon the table top. Carefully read and record 

 the length of the shadow. Is the length of the shadow more or less 

 than 1 ft.? How many square feet in the shadow on the table top? 



If the sun were not so high in the sky, would the shadow then be 

 longer or shorter than you find it to be? Would the area of the 

 shadow be greater or less? 



