LATITUDES AND LONGITUDES. 



hemisphere. The circles L L, are northern and I I, southern 

 parallels of latitude. All places situate upon any one of these 

 circles have the same latitude. The distances of N and s from 

 E Q, being 90 that is the latitude of the poles. The circles 

 N m s and N n s, drawn upon the earth from pole to pole intersect 

 the equator E Q, and all the parallels L L, II, at right angles. 

 These are TERRESTRIAL meridians. 



The latitude is, then, insufficient to determine the position of 

 any place. How, then, it may be asked, can the exact position 

 of any place be expressed ] 



4. Let us suppose that a meridian is arbitrarily selected, passing 

 through some particular place, such as the Greenwich Observa- 

 tory. We may conceive another meridian drawn upon the earth 

 east or west of that, so that the two meridians shall include 

 between them an arc of the equator,' consisting of a definite 

 number of degrees ; say, for example, that it shall consist of 20 ; 

 then such a meridian will be defined by stating that it is 20 east 

 or west of the meridian of Greenwich. All that can be settled 

 by such a statement is the position of the meridian in which the 

 place lies with reference to the arbitrarily chosen meridian of 

 Greenwich. This relative position of the two meridians is called 

 the LONGITUDE OF THE PLACE. As the meridian from which the 

 longitude is measured is altogether arbitrary, there being no 

 physical or geographical reason why one meridian should be 

 chosen rather than another, each nation has naturally selected 

 as the zero of longitude the meridian of some noted place in its 

 precincts. In England the Eoyal Observatory at Greenwich has 

 been the place selected, and accordingly in all English works 

 on geography, political and physical, longitudes are invariably 

 expressed in reference to the meridian of Greenwich. It will, 

 therefore, be most convenient for us here to refer to that 

 meridian. 



When these explanations are clearly understood, we shall be 

 in a condition, distinctly and definitely, to express the position of 

 a place upon the surface of the globe of the earth. If we state 

 its latitude and its longitude, we can fix at once, and unequivo- 

 cally, the position of a place. Thus, let us suppose that its 

 latitude is 50 north, its longitude 30 east of Greenwich ; its 

 position will be found by imagining a circle parallel to the 

 equator drawn upon the northern hemisphere at a distance of 

 50 from the equator ; then, supposing a meridian drawn 

 through Greenwich, intersecting this parallel, and another 

 drawn so as to cross the equator at a point 30 east of the 

 former ; the place in question will be upon the line parallel to 

 the equator first drawn, inasmuch as it will be 50 north of the 

 100 



