^ 



' -Ml 



\<- 



■i. 



). 



* -a 





k - 



f 



ft 



4 



.. K. 



^ 1 



i 'per 



1 - 



■^^^ tii( 



e 



■^ 

 ^ 



f 

 I 



1 



'■^- i^j ^, 



7 



1 1 



5 



r r 



V 



1 



VJ*- 



i.-A^L^ -^ 



.« 



I. 



1'-. 



tbe ' 



I 



obi ^ ; 



's * Sur- 



Sect. III.] 



HYDROGRAPHY 



71 



be the correctness of the result. It is clear that the 

 true bearing of the object at each station should b 





served (see Astronomical Bearing) ; that the course steered 

 should, if possible, be equally well known ; (this is eiFected 

 in the best manner by observing the magnetic bearing of 

 the object with the compass which directs the base, or 

 that which is to be steered by in-running the base ; at 



«r" 



ar - 



»t6r. 



the same time that its true hearing is observed ;) that the 

 distance run should be determined by patent log ; that the 

 ship should be on her course at starting when the bearings 

 are observed; and that the log should be put over and 

 hauled in at the instant of making the obseryations. If 

 the ship should of necessity alter her course during the 

 operation, it should be carefully noted, the log looked at, 

 and fresh bearings of the objects taken. 



Tvv^o observers are necessary to accomplish these ob- 

 servations nicely, and without hurry. 



AVith these data the height of the object may be found 

 with considerable accuracy,* e^-p^cially if the dip-sector be 

 used. Having determined the height of a mountain, you 

 may often find it useful to know your distance from it 

 Avlien cruising oif the coast ; and it will also aiTord amuse- 



tf - 



f. 



ment and practice to see how near you can fix the ship 

 by it, as compared with cross-bearings or other observa- 

 tions. For this purpose it will be convenient to make a 

 constant for the height, t 



^ .ill 



-; 



'\'^' 



.'.0 



Lighthouses. 



14. If lighthouses are erected upon xho coast, dczcribe 

 exactly their locality, geographical position, appearii._j, 



* See Appendix No, 2. 



f See x\ppendix No. 





