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Sect. III.] 



HYDROGRAPHY. 



7kl 



Lastly, put a meridian line 



and scale to 



the plan. 



Iu.ert the variation, geographical position, time of H. W. 

 F. and C, the low-water standard, to which the soundims 

 are reduced, and the range at springs and at neaps ; note 



the dui 

 by the 



draw leading marks and put in views, 



mountains 



If time does not permit of a regular survey being exe- 

 cuted, still a useful record may be made by an itinerant 

 survey, or even an eye sketch, assisted by sextant angles, 

 a few soundings judiciously taken, the true bearing of one 

 object and the measurement of a base by sound, or with a 

 Rochon micrometer as before-mentioned. 



Sailing Directions. 



22. Whenever a survey is executed, sailing directions 

 should accompany it, and too much care carmot be be- 

 stowed upon this important part of a surveyor's duty. 



They should contain a description of the coast (see 

 Art. 11) ; directions for making the land ; for approach- 

 ing, and sailing into or out of the port both by daylight 

 and with the aid of marks, and also by night or in thick 



weather, when the lead and the lighthouse, if there be 



must be the seaman's principal guide. How 



one 



vessel is to proceed with a leading or a beating windj 

 and with or against the tide—how far she may stand on 

 either tack— what water she may expect to find at low- 

 water springs— and how she may ascertain the depth by 

 calculation on any other day — within what limits a vessel 

 may safely steer in bad weather and when no pilot is on 

 board— where the best anchorage lies, the depth in wliich 





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