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HYDROGRAPHY, 



[Sect. III. 



temperatures ; for although limits have been assio-ned to 

 these belts of moving water, yet they vary so° much 

 according to season, and the data for defining them have 

 hitherto been so insufficient, that it cannot be said they 

 are known with any tolerable deerce of precision. 



In tbfi China Sea and among the islands of the great 



Archipelago the tides run strong and are°ery 



Lud observations are especially 



Indian 



indifferently known 

 desired at those places. 



In the southern passages it would be well to try durino- 

 the westerly monsoon, whether the equatorial current may 

 not be found pursuing a subaqueous course to the west- 

 ward, notwithstanding the surface current be found 

 running in the opposite direction. 



Upon the east coast of North America, between the 

 Gulf-stream and the coast, observations upon the set of 

 the stream are also much wanted. 



Approachina a Coast. 



Wber 



in the ocean, the temperature of the surface of the sea 

 should be more closely attended to, for it has been found 

 in many instances that after a certain shoaling of the 



water 



the surface partakes of the temperature of the 



lower strata of the sea, which are in general colder than 

 the upper. If such should be found to be the case 

 always, and if from well-authenticated facts it should 



possible to fix zones of certaui temperatures about 

 particular localities, the result would be highly useful 

 to the navigator when out in his reckoning and perplexed 

 with thick and ha^v weather. 



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