THE SUN THE CAUSE OF THE SEASONS 



285 



a figure similar to Fig. 214. Measure and record the distances be- 

 tween the two pairs of parallel lines as they strike the horizon line 

 as in the last exercise. 



At latitude 49, is 1 sq. ft. of sun's rays spread over a larger area in 

 June or December? 



State the proportion of these two areas according to your 

 measurement. 



At noon, at latitude 49, the sun heats each square foot of earth's 

 surface about how many times as much on June 21 as on December 22? 



Accurate measurements show that 1 sq. ft. of sun's rays 

 at latitude 49, are spread over about three times as large an 

 area on December 22 as on June 21. This means that the 

 earth's surface is heated only about J^ as much at noon on 

 December 22 as on June 21. 



FIG. 214. Slant of sun's rays at 

 latitude 49. 



FIG. 215. Slant of sun's 

 rays at 30 latitude. 



Exercise 67. To Study the Heating Effect of the Sun's Rays at the 

 South Boundary of the United States, Latitude 30 



At noon, on June 21, at latitude 30, the altitude of the sun in 83^; 

 at noon on December 22 it is 36^2. 



Construct accurately from these data a figure similar to Fig. 215 

 and measure the distances between the two pairs of parallel lines as 

 they strike the horizon line. 



At latitude 30, about what is the relative areas over which the 

 sun's rays are distributed on June 21 and on December 22 at noon? 



What is the relative heating power of the sun at this latitude on 

 June 21 at noon compared with that on December 22? 



What do you now say is one of the chief causes of our summer and 

 winter seasons? 



Judging from the foregoing exercises, should we expect greater 

 temperature differences between summer and winter in Texas 

 or in North Dakota? Explain clearly your answer. 



