32 



FIEST TEAR SCIENCE 



the sun's shadow and note accurately the time the shadow fell on this 

 line. On the next day note the time the shadow falls upon the same 

 line. If your watch is right, the difference in time it shows between 

 the falling of the shadows the first and the second days is the differ- 

 ence between this particular solar day and the mean solar day. This 

 may be nearly a minute. The shortest shadow of the day marks 

 noon. It extends north and south. (Your watch keeps mean solar 

 time. But twelve o'clock by your watch will probably not be mid- 

 day or high noon, as your watch is set to Standard Time.) 



15. 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 lati- 

 tude, and through these points 

 of division are passed circles 

 parallel to the equator. These 

 circles gradually decrease in size 

 as they approach the poles. They are called parallels of 

 latitude and are numbered from at the equator to 90 at 

 the poles. 



A certain one of the meridians, usually the one passing 

 through Greenwich, England, is called the prime meridian 

 and numbered 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 out- 

 line 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 



Fig. 12. 



