is 



ELEMENTS OF GENERAL SCIENCE 



(dining through the hole might be the same in both experi- 

 ments, but in the morning it is distributed over more surface 

 and is therefore less intense. If you spread your butter over 

 a larger piece of bread, it will be spread thinner. 



Of course, the difference that you have discovered between 

 morning and noon exists between winter and summer. Can 

 you make a drawing showing exactly how large a space will 

 be covered by a beam of sunlight one inch square if it comes 

 to the earth at an angle of 65 s ? of 18 ? In which case 



would the earth's surface 

 receive more heat to the 

 square inch ? How much 

 more ? Which corre- 

 sponds to summer? to 

 winter ? 



18. Length of day and 

 night. In summer, when 

 the sun is higher in the 

 heavens, it is also visible 

 more hours in the day. 

 The difference between 

 the longest day and the 

 shortest one is not the 

 same at all places. It is 

 least at the equator and greatest at the poles. At inter- 

 mediate places the difference corresponds to the distance 

 from the equator. In the central part of the United States 

 (central from north to south) the longest daylight, in the 

 latter part of June, is about fifteen hours, and the shortest, 

 in the latter part of December, is about nine and one-half 

 hours (fig. 16). 



The angle of the sun's rays and the number of hours dur- 

 ing which it shines upon us work together to make the earth 

 and the air warmer in summer than in winter. From an 

 almanac it is possible to find out the length of day on the first 



FIG. 15. Heating effects of sun's rays 



Diagram showing the difference in inclina- 

 tion of the earth's surface to the sun's rays. 

 A sunbeam of the given size would cover 

 more area at B than at A 



