POSITION OF A PLACE. 



equator, and it will be also in the meridian last drawn, inasmuch 

 as it will be 30 east of Greenwich. Since, then, it will be at 

 the same time on both these lines, it will necessarily be at the 

 point where they cross each other at the east of the standard 

 meridian of Greenwich. 



5. Thus, then, we have succeeded at least in establishing stand- 

 ards of position and a nomenclature by which the exact position 

 of a place on the surface of the globe can be expressed. But we 

 have still another much more important and difficult question to 

 settle. How are we to discover in what part of the globe any 

 place is which we may occupy at a given time ; in other words, 

 how are we to discover its latitude and its longitude ? These 

 are questions, especially the latter, attended with some difficulty, 

 and which have been solved by different methods, applicable in 

 different cases, according to the circumstances under which the 

 position of the place is sought, and the purpose for which such 

 position is to be determined. 



At any place on land where the geographical position is once 

 determined, it may be recorded, so as to be permanently known 

 for the future without a repetition of the process for determining 

 it ; but it is otherwise at sea. On the trackless surface of the 

 deep all marks of events and operations are immediately oblite- 

 rated, and a new investigation must be instituted in every ease 

 when the position of any point is to be determined. The mariner 

 must, therefore, be supplied not only with the means of deter- 

 mining the position of his ship at all times, but with means the 

 application of which is practicable under the peculiar circum- 

 stances in which he is placed. The instruments he uses must 

 not only be portable, but must be such as may admit of being 

 manipulated, subject to the disturbances and the vicissitudes of the 

 sea. The objects of his observations must be such as are almost 

 always in his view. It is evident, then, that the problem, as 

 applicable on land, is wholly different in its circumstances and 

 conditions from that which is applied on the deep. But even on 

 land the problem presents itself under various circumstances and 

 conditions. In the fixed observatory, where the observer is 

 supplied with instruments of the greatest magnitude, of the most 

 refined accuracy, and the most absolute stability, methods have 

 been used which are susceptible of the last conceivable degree 

 of accuracy, and accordingly the position of those points on the 

 globe where such observatories have been erected are usually 

 determined with the greatest degree of precision. Such points 

 on the globe serve, therefore, as a sort of landmarks, relative 

 to which the position of all surrounding places may be deter- 

 mined. 



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