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Sect. III.] 



HYDROGRAPHY 



77 



tions which lie in a curve concave towai^ds yon^ since cases 

 will often arise when stations m situated will give very 

 inaccurate results, as with the 



plate A, 



20. While operations on shore are going forward, boat 



objects A H I at p in 



can be sounding out the harbour, and fixing the points of 

 reefs, rocks, &C.5 bearing in mind that it will always be 

 found more satisfactory to land upon every rock or point, 

 &c,, than to lie off in the boat, and fix them by estimated 

 distances or by intersections, either from these or from 



other stations. 



In sounding, fix the boat at starting by two sextant 

 angles ; note the direction in which it is intended to run 

 out the line of soundings, and note any two objects distant 

 fi:*om each other, that are in a line upon that bearing, or 



if the port be not too extensive make use of staves with 



flag 



"^ 



shifting them along the coast at the end of each line 



of soundings the exact distance it is intended to run 

 them apart — the boat showing a signal when the flags 



sound at regular 



are to move ; then keep the marks on, and ; 

 intervals 6, 5, 4, 3, 2, or fewer casts in a minute accordin 

 to the depth ; and at given short intervals note the time 

 and fix the position of the boat by two angles as before- 

 mentioned,* as also whenever there is any material alter- 

 ation in the depth, or whenever the number of casts 



alters in a given time. When 



line fix the boat's position, and alter the course, sounding 

 all the time until far enough for running back the second 



line of soundings parallel with the first. Fix the boat's 



* See the form in Appendix for entering these angles and soundings^ 

 No. 4. 



