252 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



The systems of time in various countries — Continued. 



This table makes easy not only the transformation of a given time 

 to the corresponding time at Greenwich but also its conversion to 

 that of any other place. For instance, when it is 6 horns a. m. in 

 Chicago, in Manila it is 6 + 6 + 8 = 20 hours, or 8 hours p. m. 



Upon the terrestrial map given here, the 24-hour zones have been 

 indicated; the central line of the first passes through Greenwich. 

 The countries and territories which have not yet adopted the inter- 

 national system of time are tinted blue, the others rose. For great 

 extents of country like the United States of America it is easy to see 

 at a glance the time in each region. 



THE INTERNATIONAL DATE LINE. 



It is well known that if we go westward from America to Asia, 

 we find our date one day behind time when we reach Asia; if we 

 travel eastward over the same route we find out* date one day ahead 

 of time when we reach America. 



In order to avoid this confusion of dates, it is customary, in cross- 

 ing the one hundred and eightieth meridian from Greenwich, to 

 "jump" a day, if traveling toward the west, and to repeat a day if 

 traveling toward the east. However, because of geographical and 

 political conditions, the international date line does not coincide 

 exactly with the one hundred and eightieth meridian. It is an 

 irregular line so situated that all eastern Siberia has the same date, 

 the Aleutian Islands and Hawaii the same date as the United States 

 of America, and, finally, the Fiji Islands and Chatham Island that 

 of Australia. This line is shown on the accompanying map. 



