86 EXPERIMENTAL GENERAL SCIENCE 



a place. The angle at which the sun's rays are received have 

 an important bearing on the subject. The amount of heat 

 sent us by the sun does not change materially from day to 

 day. When the sun is directly overhead, the heat energy 

 falling on each square centimeter is about 1% calories a min- 

 ute, summer or winter. Owing to the shape of the earth, how- 

 ever, and the direction of its axis, that part of its surface out- 

 side of the tropics always receives the rays in a more or less 

 slanting direction, and the heat and light are in consequence 

 distributed over a greater area. Nevertheless, at the time of 



FIG. 29. Distribution of heat rays at morning and night. 



the summer solstice when the longest period of daylight occurs 

 in the Northern Hemisphere, the north pole receives much 

 more heat than the equator. Owing to the evaporation of the 

 ice and snow, however, it is not correspondingly heated. The 

 region of greatest heating at that time is near the latitude of 

 Chicago and Buffalo (152). 



81. The Lag in Temperature. The longest day in the 

 Northern Hemisphere is in June and the shortest is in Decem- 

 ber, but June is seldom if ever our hottest month or December 

 the coldest. Moreover, since the sun is more nearly overhead 

 at noon than at any other time, noon should be the hottest part 



