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HEAT 



ter inch hole made in the center. The line of divisions 

 represents the surface of a small part of the earth ; the 

 movable piece represents a sunbeam one inch wide. 



When this "sunbeam" is perpendicular to the ''surface 

 of the earth" it covers one inch. How many degrees 

 are needed between two lines to make them perpendicular 

 to each other? If the "sunbeam" is at any other angle 

 it covers more than one inch of the "surface of the earth." 

 Now if you had just enough butter to cover one slice of 

 bread but had to cover two slices with it, how thick 

 would the butter be? Suppose that you were so un- 

 fortunate as to be obliged to cover three slices with the 

 same amount of butter, how thick would the butter be? 

 In a manner similar to this the sunshine is spread "thick 

 or thin" upon the surface of the earth, as the height of 

 the sun varies with the time of day and with the changes 

 of season. 



b. Place your apparatus in the sunshine early in 

 the morning, or late in the afternoon, in suc;h a manner 

 that the movable arm "sunbeam" may be aimed at the 



