32 



OUR OWN WORLD 



Meridians and Parallels of Latitude. For purposes 

 of measurement, circles of any size are divided into 360 

 equal parts called degrees. Thus the equatorial circle of 

 the earth is divided into 360 parts. Through each of these 

 divisions there is a semicircle drawn from pole to pole. These 

 semicircles are called meridians. Each meridian is divided 

 into 180 parts called degrees of latitude, and through these 

 points of division are passed circles parallel to the equator. 

 These circles gradually decrease in size from 25,000 miles at 

 the equator to points at the poles. They are called parallels 



of latitude and are numbered 

 from at the equator to 90 at 

 the poles. (Figure 11.) 



A certain one of the meridians, 

 usually the one passing through 

 Greenwich, England, is called 

 the prime meridian and num- 

 bered 0. East and west of this 

 the meridians are numbered 

 from 1 to 180. The degrees 

 thus numbered are called degrees 

 of longitude. Thus we have a skeleton outline by means 

 of which we are easily able to locate the position of any 

 place upon the earth. To secure greater accuracy than 

 could be obtained by giving merely the degrees of latitude 

 and longitude, each of these degrees is divided into 60 

 equal parts called minutes, and each minute can be divided 

 into 60 parts called seconds. 



The Measurement of Time. Experiment 6. On a fair day 

 place a sundial in an exposed position, and after carefully adjust- 

 ing it, compare its readings with those of an accurate watch. Unless 

 you are on the time meridian, the readings are not alike. 



FIGURE 11. MERIDIANS AND 

 PARALLELS OF LATITUDE 



