74 



HYP ^ '^ G R APHY 



[Sect. III. 



1 



Sect 



III 



place, by persons who probably never contemplated the 

 performance of such an undertaking, it may be usefiil 

 to describe as briefly as possible the process. Make 

 choice of two stations at as great a distance apart as 

 the survey will admit of, and from which the eye can see 

 over a considerable portion of the ground to be mapped 

 as A, B, plate A. Put up marks or select objects 

 at all convenient places around the survey, so as to be 

 able to form a network of triangles over the whole space 

 and include every conspicuous feature around, such as 

 hills, cliffs, rocks, and especially objects at, or near, high- 



,.'n€ 



water maric„ 



Jtlavin 



D 



upon these marks, as at A 



? 



c 



■shore if there be a convenient spot at hand ; but it would 

 be Useless to devote much time to this purpose, for the 

 survey of a port in general does not so much require that 

 the absolute distances between places should be accurately 

 known, as that the angles should he carefully observed, 

 and therefore the relative distances preserved. If it be 



X 



hecessary to measure a short base of a quarter or half a 

 mile, and the ground be uneven, plant staves (boarding- 

 pikes) in the line to be measured, and stretch the lead 

 line along from pike to pike in the direction of the wire 

 of the thoodolite v/hen levelled; and inpasure along the 

 line with a tape, or with rods ; then shift the pikes and 

 ine on, until the rL.niired distance has been measured, 

 the length of which should not be less than l-7th of the 



distance between the objects, the distance of which is re- 

 quired. 



If a micrometer be on board, a very fair base may be 



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