THK L,VT!THjr. AM) U>SU!TI UK*. 



TltE LATITUDES ANT) LONGITUDES. 



BEFORE it is possible to acquire a distinct knowledge of the position or dis- 

 tances of any bodies in the universe outside the surface of the earth, it is first 

 indispensable that we, who have to make these calculations, should distinctly 

 ascertain our own position in refer3nce to the bodies we observe. But as our 

 position is subject to continual change, as well by reason of the diurnal rota- 

 tion of the earth upon its axis, o.i the surface of which we are carried round, 

 us the annual motion of the globe in its orbit round the sun, we are obliged as 

 a necessary preliminary to analyze with accuracy all the circumstances of 

 these motions. But even befoi 3 we are in a condition to accomplish this, 

 there is another prelimir ary e.cp not less indispensable, which is to ascertain 

 our own position on the surface of the globe we inhabit. 



This is not so easy a mat er as at the first view it might seem to be. The 

 earth we dwell on is a ^..o; i of stupendous magnitude. The range of our 

 vision around any sitratic.i vhich we may occupy upon the surface of this 

 globe is small. In the rrcc-. unobstructed situation we can obtain that which 

 is presented us at sea, when out of sight of land, on the clearest day our ob- 

 servation 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 ? 



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 sur- 

 face of the earth where the axis on which it performs its diurnal rotation ter- 

 minates, and they are distinguished as is well known by the names of the north 

 and scuth poles. 



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