LATITUDE AND LONGITUDE. 



505 



If we send a skittle ball rolling we perceive it turns round as it proceeds. 

 So the earth rotates on its axis, N s, in the accompanying diagram ; the 

 extremities of the axis are called the poles. The line in the middle is the 



Fig. 53 j. KviJonce of the spherical form of tiic earth. 



equator, which is divided into 360 equal parts, each being 69^ miles in 

 length ; so there are 180 lines, or rings, drawn upon the globe from N to S, 

 and these are meridians. In England the degrees are calculated from 

 the Greenwich meridian. We can thus obtain the distance of localities east 

 or west, as we may briefly show (fig. 554). 



The distance of any meridian from the first meridian is termed the 

 longitude, and it is employed in describing 

 the situation of a place on the earth's sur- 

 face. Suppose L (fig. 554) a city, its 

 longitude will be 30, since it lies on a 

 meridian which is 30 from the first. 

 So, for example, the longitude of Oporto 

 is 8 37' west, Paris 2 22' east, Vienna 

 1 6 1 6' east, Bagdad 44 45' east, reck- 

 oned from the meridian of Greenwich, 

 and so on. At the iSoth degree we have 

 proceeded half round the globe, and reached 

 the farthest distance from the first meri- 

 dian, and are now on the opposite side of 

 the earth, and proceeding in a similar 

 manner in the opposite direction we get 

 west longitude. 



It will readily be perceived that a knowledge of the longitude alone is 

 not sufficient to determine the situation of a place on the earth's surface. 



Fig. 554- Latitude and Longitude. 



