THE LATITUDES AND LONG ITU 1; 



When these explanations are clearly understood, we shall 1* in a condition. 

 distinctly and definitely, to express the position of a place upmi the Mirl: 

 the globe of the earth. If we state its latitude and its longip,: f, x 



at once, and unequivocally, the position of a place. Thus, let us snppus- t!r,,t its 

 , latitude is 50 north, its longitude 30 east of Greenwich; its position will l,e 

 ; found by imagining aline parallel to the equator drawn upon the m.rthern hem- 

 } isphere at. a distance of 50 from the equator; then, supposing a meridian 

 ) drawn through Greenwich, intersecting this parallel, and anothe/drawn so as 



* to cross the equator at a point 30 east of the former; the place in i;n 



S will be upon the line parallel to tho equator first drawn, inasmuch : , s it will be 

 I 50 north of the equator, arid it will be aleo in the meridian last drawn, inas- 

 much as it will be 30 east of Greenwich. Since, then, it will be :u the same 

 / lime in both these lines, it will necessarily be at the point when? thev 

 , each other at the' east of the standard meridian of Greenwich. 

 ^ Thus, then, we have succeeded at least in establishing standards of position 

 ) and a nomenclature by which the exact position of a place on the surf;. 

 I the glebe 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 question 



pecially the latter, attended with some difficulty, and which have 

 solved by different methods, applicable in different cases, according to the cir- 

 cumstances under which the position of the place is sought, and the pnrp<> M . 

 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. ( )n the 

 trackless surface of the deep all marks of events and operations are immedi- 

 ately obliterated, and a new investigation must be instituted in every case when 

 the position of any pcint is to be determined. The mariner must, therefore, 

 be supplied not only with the means of determining the position of his ship at 

 all times, but with means the application of which is practicable under the 

 ( peculiar circumstances 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 object 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 Cir- 

 cumstances and conditions from that which is applied on the deep. Uut even 

 on land the problem presents itself under various circumstances and conditions. 

 ? In the fixed observatory, where the philosopher is supplied with instruments 

 ( of the greatest magnitude, of the most refined accuracy, and the m.)>t absolute ^ 

 ; stability, methods have been used which are susceptible of the last conceiv- ( 

 \ able degree of accuracy, and accordingly the position of those points un the 

 globe where such observatories have been erected, are usually determined with 

 the greatest degree of precision. Such points on tho globe serve, therefore, 

 as a sort of geographical landmarks, relative to which the position of all sur- 

 rounding places may be determined. 



The circumstances under which the scientific traveller and geographer makes 

 his observations, with a view to the general determination of the points of a 

 country, are less favorable to accuracy than those available to the astronomer, 

 but still are more susceptible of precision than those which can be pi a-.-d at 

 the disposal of the mariner. It is, however, the business and the duty of those 

 who devote their lives to the advancement of the sciences, to supply to each 

 of observers those instruments and methods of inquiry which are capable, respeyt- 



