You know that latitude is the distance, in degrees, north or south of the Equator. For instance Greenwich is marked 51 degrees north. Any place on the Equator had a latitude of zero degrees; that is, none at all. The poles are 90° north or south as the case may be. Longitude is measured in the same way. But there is no Equator running around the world from north to south. So it had been agreed by the nations that one of the meridians is to be called the Prime Meridian. This meridian has zero longitude. A point 10 degrees east of it is called 10° E.; a point 10 degrees west is called 10° W. What is the longitude of New York? The Prime Meridian runs through Greenwich, England, 5 miles from London. Here is located an observatory. A telescope here is so arranged that exactly at 1 o'clock P. M. every day a big colored ball falls from a tower. The clock which you see sets itself at exactly 1:00 P. M. This time is telegraphed instantly to many parts of the world, and all standard clocks are set by it. It is very necessary that time in all parts of the world be regulated. When it is 1:oo P. M. in Greenwich, England, the clocks 180 degrees distant should show 1 A. M. Why? New York time is 4 hours earlier than London time. Why? Chicago time is 1 hour earlier than New York time. Why? What time is it in London now? Greenwich is on the Thames below London. From the observatory can be seen miles of shipping in the Thames. The great English fleet is frequently assembled near here for review. How many time belts are there in the United States? What time is it now in Calcutta? Keystone ID: 6146 Note: All titles, descriptions, and location coordinates are from the original Keystone Slide documentation as supplied by the Keystone View Company. No text has been edited or changed.