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Sect. III.] 



HYDROGRAPHY. 



6" 



8. If near to any shore, a few points of which are well 

 fixed, and the water he found too deep for anchorage, the 

 course of the stream may still be ascertained by notin 

 the drift of a float — a plank, for instance, weighted at 

 one end, so that the other just floats above the surface ; 

 or a weighted lo.reca^ — fixing its position from time to 



time by angles taken in a boat at the several places, and 

 noting the intervals by a watch. 



Such methods may of course be resorted to when cir- 

 cumstances do not admit of greater accuracy, but when- 

 ever it can be done, the course and rate of the stream^ 

 should be observed every hour during both tides, and the 

 times of slack water carefully noted, by anchoring a boat 

 or vessel. Upon an open coast one set of such observa- 

 tions made here and there, well clear of the headlands, 

 will be sufficient ; but in chaimels and straits in which the 

 tide enters at both extremities the tidal phenom-cna are so 

 varied and full of interest, that it becomes highly im- 

 portant^to spread the observations over as large an extent 

 of the channel as possible, and to pursue a regular system 

 of hourly observation throughout both the ingoing and 



outgoing stream.s. 



It is desirable to know at each place the time of slack 

 water, the direction in which the stream turns, and the 

 rate and course at wliich it runs during its several stages. 

 The stations should be numbered, and the times all 

 referred to one meridian. In such channels there will 

 probably be one or more places where the stream.3 meet, 

 and there of course observations v>dll be made ; and as 

 one of these places will probably be the virtual head of 

 the tide wave, it may so happen that the time of the high 



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