LATITUDES AND LONGITUDES. 



motions. But even before we are in a condition to accomplish 

 this, there is another preliminary step not.less v indisp^nsable, 

 \vhich is to ascertain our own position on the surface of the globe 

 we inhabit. 



This is not so easy a matter as at the first view it might 

 seem to be. The earth we dwell on is a globe which com- 

 pared with any familiar standards of measure has a stupendous 

 magnitude. The range of pur vision -around any situation which 

 we may occupy upon the surface of this globe is small. In the 

 most unobstructed situation we can obtain that which is pre- 

 sented us at sea, when out of sight of land, on the clearest day 

 our observation is circumscribed by a radius of a few miles. 

 The portion of the surface which we see at one and the same 

 time, forms in reality so small a patch of the globe of the earth, 

 that it is only by indirect reasoning that we can recognise upon 

 it any character save that of a flat plane. How, then, are we to 

 know in what part of the terrestrial globe that small patch of 

 surface is situated ? 



2. To answer this question, it is evidently necessary first to 

 settle some fixed points or lines to which we may refer various 

 places, and by which we may express their positions. The points 

 which have been usually selected for this purpose are the POLES 

 and the EQUATOR. The poles are those points on the surface of 

 the earth where the axis on which it performs its diurnal rota- 

 tion terminates, and they are distinguished, as is well known, by 

 the names of the NORTH and SOUTH poles. 



If we imagine a circle drawn round the globe in such a manner 

 as to divide it into two hemispheres, having in the midst of one 

 the north pole, and in the midst of the other the south pole, 

 such a circle is called the EQUATOR, from equally dividing the 

 globe. Every point in this circle will be at the same distance 

 from the poles, and if we imagine the globe to be cut by a plane 

 through the poles, that plane will be at right angles to this 

 circle, and the section it forms will be what is called a TERRES- 

 TRIAL MERIDIAN. The arc of this meridian between either pole 

 and the equator will be one quarter of its entire circumference, 

 and will therefore be 90. The equator is, therefore, everywhere 

 90 from each of the poles. 



In fig. 1, N is the north and s the south pole, and EQ is the 

 equator. 



The hemispheres into which the equator divides the earth are 

 called the NORTHERN and SOUTHERN HEMISPHERES. That which 

 includes the north pole, being the northern, and that which 

 includes the south pole, the southern. 



The position of a place in either hemisphere with reference to 

 98 



