REMARKS ON CURRENTS. 205 



parts are either at rest, or have a different motion : 

 and an under current is where a deep stratum of 

 water moves in a different direction from that at 

 the surface. 



Hence where the motions in the water are so va- 

 rious, there must evidently be great uncertainty 

 in the usual methods of ascertaining the set and 

 velocity of currents in deep seas. Superficial and 

 bodily currents, indeed, may be discovered by their 

 effects on the progress and course of vessels sailing 

 in them, or by their influence in conveying wood, 

 fruit, and other produce of one country, to the 

 shores of another ; as also in conducting buoyant 

 articles, cast into the sea, in known situations, to 

 remote regions, where they may be recognized. 

 And, in shallow water, or wherever the depth is 

 such as to be fathomed with sounding lines, a heavy 

 body, with a line attached, being sunk to the bot- 

 tom, shows, by the relative motion of a boat at the 

 surface, to which the weight acts as an anchor, the 

 true set and velocity of the current. As, however, 

 there are doubtless under currents, as well as super- 

 ficial and bodily currents, it is evident that the 

 usual method of sinking a heavy bulky body, such 

 as an iron kettle, mid-way in the sea, and connect- 

 ing it by a line to a boat, and thus forming the 

 kettle into a sort of floating anchor, and estimating 

 the set and velocity of the current by the motion of 

 the boat through the water, cannot be depended on 

 for discovering the real nature of the current, but 



