THE SUN THE CAUSE OF THE SEASONS 



283 



If the sun were higher in the sky, what would then be true? 



How does the altitude of the sun affect the length and area of the 

 shadow? 



Do you see that if it were not for the cardboard 1 ft. square, or 

 1 sq. ft. in area, the sun's rays would fall upon that portion of the 

 table top which is covered by the shadow? 



^> 



FIG. 211. Measuring the board's shadow on December 22, at latitude 

 40, North. 



Would the energy in 1 sq. ft. of sun's rays fall upon a larger or 

 smaller area of table top if the sun were at a lower altitude? 



What would be true if the sun were at a higher altitude? 



When 1 sq. ft. of the sun's rays is spread over a large area, is that 

 area heated more or less than when the rays are spread over a small 

 area? 



Exercise 65. To Construct Figures Representing the Effect of the Sun's 

 Altitude upon the Length of Shadow 



1. With a ruler, lay off a horizontal line to represent the table top. 

 Then, using a protractor and ruler, draw a second line slanting at an 

 angle of 73>2 down to this line (Fig. 



212). This is the angle of the sun's 

 altitude on June 21 on the 40 north 

 latitude. Draw a third line parallel to 

 the second line and the width of your 

 ruler from it. 



2. In a similar manner, construct 

 two parallel lines the width of your 

 'ruler apart and slanting at an angle of 

 26^ to the horizon line as in Fig. 212. 



This is the angle of the sun's altitude on December 22 at the 40 

 north latitude. 



3. Now measure accurately along the horizon line the distance 

 between the pairs of parallel lines in each case. How does the dis- 



FIG. 212. Slant of sun's rays 

 at 40 latitude. 



