LONGITUDE AND TIME 183 



This is because man has agreed to a sort of artificial noon more 

 suitable to his interests. Since the sun is steadily moving 

 westward, true noon does the same, and if the sun time were 

 used, the time at even nearby places would not be the same. 

 To facilitate the running of trains and other work depending 

 upon exact time, the surface of the earth has been divided 

 into time belts, each 15 degrees wide, in which the clocks record 

 time alike. When it is true noon over the center of such a 

 time belt, it is assumed to be noon throughout the belt, though 

 in some parts it is earlier and in others later than noon. 

 There are five of these time belts in North America which, 

 beginning in the east, are known respectively as Intercolonial, 

 Eastern, Central, Mountain and Pacific time. Time, according 

 to this arrangement, is known as standard time. The meridians 

 that form the centers of the time belts are the 60th, 75th, 90th, 

 105th, and 120th west of the meridian of Greenwich. When 

 a traveller passes from one time belt to another, he sets his 

 watch forward or backward an hour, according to the direc- 

 tion in which he is traveling. Were it not for the time belts, 

 his watch, on comparison with local time, would seem to be 

 constantly gaining or losing time. The old abbreviations, 

 a.m. for ante-meridian, and p.m. for post-meridian, have thus 

 lost to some extent their significance since the adoption of 

 standard time. 



152. The Earth's Axis and the Zones. The earth's axis 

 is not at right angles to a line drawn from the sun to the earth, 

 but is tilted 23^ degrees from the perpendicular. In con- 

 sequence of this, the north pole is inclined toward the sun 

 during our summer season and away from it in winter. Ex- 

 actly half of the earth is always toward the sun, but because 

 of the tilted axis, the sunshine lacks 23^ degrees of reaching 

 the south pole in summer, while it shines 23}^ degrees beyond 

 the north pole. In winter these conditions are reversed. 

 Though first one pole and then the other is inclined toward 



