THE EARTH'S PLACE IN THE UNIVERSE 29 



months and days, has been changed twice since the time of 

 Julius Caesar. These changes were necessary because of 

 the neglect of a few seconds in calculating the length of a 

 year. If the calendar had not been corrected, certain 

 religious festivals would by this time be observed about a 

 month later by the calendar than the seasons in which 

 they originally occurred. 



20. Longitude and Time. The meridians of longitude 

 on maps and globes correspond to the celestial meridians; 

 that is, the meridian of longitude of a given place lies directly 

 under the celestial meridian of that place. For example, the 

 meridian of 90 west longitude which passes through 

 Memphis, Tenn., Jackson, Miss., and New Orleans, La. 

 lies on the earth directly under the celestial meridian of 

 those three places. The meridian passing through Green- 

 wich, England, has been adopted by all countries of Europe 

 and the Americas as the prime meridian, or the meridian of 

 longitude. Places within 180 west of the prime meridian 

 are in west longitude; places within 180 east are in east 

 longitude. The national observatory of the United States, 

 the Naval Observatory at Washington, is situated 77 west 

 of the prime meridian, therefore at 77 west longitude. 

 Delhi, in northern India, is situated about 77 east of 

 Greenwich. 



When the sun crosses the meridian at Washington, it is 

 noon there. It is after noon at places east of Washington 

 and before noon at places to the west. In twenty-four hours 

 the sun will again be overhead at Washington, having 

 (apparently) passed westward around the earth 360. 

 In each hour, then, it passes over 15. When it is noon 

 at Washington, it is 1 p. m. at a place 15 east of 

 Washington, and 11 a. m. at a place 15 west of Washing- 

 ton. If 15 cause a difference of 60 minutes of time, 

 1 degree will cause a difference of 4 minutes. 



News of an event which occurred at 1 p. m. in Washington 



