THE EARTH'S PLACE IN THE UNIVERSE 31 



all our government timepieces in any one belt have given 

 the same time at any moment. When the government 

 made the change in all post-offices, custom-houses, and naval 

 stations, people had to make the same change for their own 

 convenience, and now Standard Time is used everywhere 

 in this country. A similar plan of time belts has been 

 adopted in Europe also. 



Only the middle of a belt has the true time by the sun; 

 other parts of the belt differ from the sun's time by periods 

 varying from one to thirty minutes. Most people do not 

 know that Standard Time is not the same as sun time. 



The United States is divided into four time belts, called 

 the Eastern, Central, Mountain, and Pacific belts. Every- 

 where in a given belt the clocks are an hour ahead of those 

 in the next belt west, and an hour behind those in the next 

 belt east. When it is noon (Standard Time) at New York, 

 it is 11 a. m. in Chicago, 10 a. m. in Denver, and 9 a. m. in 

 San Francisco. It is then 5 p. m. in London. 



EXERCISES 



1. How are the south, east, and west points of the compass deter- 

 mined? 



2. '(a) How many degrees from the equator was Commodore Peary 

 when he reached the north pole? (6) How many degrees, or what part 

 of a circle, was the distance from his horizon to the North Star? (c) 

 How many degrees above the north point on the horizon, is the North 

 Star seen at the place where you live? At New Orleans? At Sitka? 



3. What is meant by the earth's period of rotation? 



4. (a) What fraction of the surface of the earth is illuminated by 

 the sun at one time? (6) Why does the lighted space move to the 

 westward? How many degrees per hour does it move? Why? 



5. (a) If the sun rises at 6 a. m. at places on the 72d meridian 

 W. longitude, at what meridian will it rise an hour later? (6) At what 

 longitude will the sun be setting when it is rising on the 90th meridian 

 W. longitude? 



6. How many degrees north of the equator is the sun when it is 

 visible for twenty-four hours at 70 N. latitude? 



