284 



THE SEASONS CLIMATE AND HEALTH 



tance between the second pair of parallel lines compare with the 

 distance between the first pair? 



EXPLANATION. Now if we imagine two bundles of rays, each 

 bundle being 1 ft. square, as coming from the sun and falling upon 

 the earth, the first at an angle of 73^ from the horizon and 

 the other at 26^, we shall see that the second bundle of rays 

 will be spread over a much larger space than the first bundle. 



SUN SETS 



T.tQ P.M 



FIG. 213. Showing the different positions, of the sun at sun rise, at noon, 

 and at sun set on June 21 and on December 22 at 40, North latitude. 



Careful measurement shows that the second is spread over just 

 about twice as much space as the first. This means that at 

 noon the sun heats 1 sq. ft. of the earth's surface and hence of 

 the earth's atmosphere but one-half as much at the 40 

 latitude on December 22 as it does on June 21 (Fig. 213). 



Exercise 66. To Study the Heating Effect of the Sun's Rays at the 

 North Boundary of the United States, Latitude 49 



On June 21, the altitude of the sun at noon at 49 north latitude is 



; on December 22, it is but 17^. 

 Following the plan pursued in the last exercise, construct accurately 



