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Sect III.] 



HYDROGRAPHY 



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construction of the vessels employed and the means they 

 have of advancing against the stream, &c., and the dis- 



e 



tance to which navigation is practicable^ severally for ves- 

 sels, boats, or barges. 



In large rivers communicating with the sea note the 

 facihty of access and egress, the depth of water on the 

 bar, if there be one,* the position and nature of shoals or 

 rocks, and the navigable capabilities of the stream, th 

 rate and duration of flood and ebb, that is, of the ingoing 

 and outgoing stream. The distance to which the stream 

 runs up, and the extent to which the rise and fall of the 

 water is felt, or what may properly be called the end of 

 the tide ; and here always, if possible, determine the ele- 

 vation of the high-water line above the mean level of the 



ocean. 



Lastly, in speaking of rivers, let it be understood that 

 the right or left bank should have reference to the do^vii- 

 ward direction of its course, so that, when descending the 



stream, the right bank is on the right hand and rn.ce versa. 

 It is better to adopt this phrase than to say east or west, 

 which might at the least be ambiguous, for it is dear that 



if a stream meander much, its course being always of 



necessity downwards, it might be successively diverted to 

 every point of the compass. 



Lakes, 



33. Lakes, properly so called, or which have no rivers 

 running through them, can scarcely ever be turned to the 

 uses of hydrography, except when they are upon a level 



* What has been already said on leading marks, lighthouses, beacons, 

 buoys, &c., &c., of course applies here also. 





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