72 INTRODUCTION TO GENERAL SCIENCE 



The United States is divided into four time belts, each 15 

 wide, and each belt takes the time of its center meridian for 

 all parts of the belt. This makes the maximum difference 

 between standard time and local time one half an hour. 

 Local time is not used except in astronomy. 



References: 



1. 1002:226-242, Time. 



2. 1304 : 404-405. Longitude and Time. 



3. 1803 : 5. The Standard Unit of Time. 



a. 1001 : 33-36. Different Kinds of Time. 



b. 1001 : 36-41. Determination of Time. 



c. 1003:48-55. Time. 



d. 1309 : 28. Sidereal and Solar Days Standard Time. 



e. 1310 : 313-314. Longitude and Time. 

 /. 1311:26-27. Time. 



g. 1312 : 30-32. The Day Standard Time. 



52. THE SEASONS 



Every one is familiar with the change of seasons, although 

 perhaps only a few have noticed the cause of the changes. 

 The weather is warmer in summer than in winter for the same 

 reason that there is a higher temperature at the equator than 

 at any other place on the earth. The more nearly vertical 

 the rays of the sun are, the more energy is received per square 

 foot. To put it another way, the more nearly the sun is 

 overhead, the warmer it is, at the surface of the earth. The 

 reason that the sun appears higher in the sky during the 

 summer is because the axis of the earth is inclined 23 J to its 

 path around the sun. Since the north end of the axis always 

 points in one direction, to the North Star, the sun seems 

 to mount higher in the sky when the earth is in such a position 

 that its axis points the north end in the general direction of 



