60 



HYDROGRAPHY. 



[Sect. III. 



...t. IJ 



Seo 



Trade drift, and Equatorial current ; the Mexican current, 

 passing along from Panama to the Gulf of California, 

 according to the monsoon. The counter- currents north 

 and south of these, and the moving belt along the coast 

 of Japan and Corea to Kamtchatka — in the great Pacific 

 Ocean ; particularly noting, as of great importance to 

 navigation, the limits of the outer currents around the 

 Cape of Good Hope and Cape Horn, all of which will be 

 found on a small scale delineated in a eeneral chart at 



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tlie end of this paper. 



Some of these currents maintain a constant difference 

 of several degrees between their own temperature and 

 that of the mean state of the water about them, and all 

 observations which can throw light upon this subject, and 

 upon the limits, course, and velocity of the stream, will 

 be most acceptable. 



6. In ]jassing through any of these great currents, the 

 observer should carefully define the extent of the belt of 

 moving water at the parallel in which he crossed it ; the 

 irait of the eddy on either side of it ; determine the rate 

 and set of both ; carefully note every barometrical or 

 therm.ometrical change of the air, or alteration in the 

 temperature or specific gravity of the sea, and if possible 

 the depths to wMch these temperatures extend; and 



record all appearances and changes which may app-^-u- 

 of interest or seem to be useful to those who mav follow 



over the same ground. 



To detect the motion of the stream the remarks in 

 Art. 2 blvmld be attended to, with the exception that 



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during the day by astronomical observation, and 



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