166 Messrs. Carpenter and Jeffreys on [Dec. 8, 



to the movement of the drag ; and the retardation of the movement of the 

 boat would he less, though still considerable. — If, again, the stratum in which 

 the "drag" is suspended should itself be moving in the direction of the 

 surface-current, but at a reduced rate, there will still be a resistance to the 

 movement of the " drag " at the more rapid rate of the surface-current ; 

 and this resistance will produce a proportional retardation in the motion 

 of the boat. — Finally, if the stratum in which the " drag " is suspended, 

 with the intermediate stratum through which the suspending line passes, 

 move at the same rate with the surface- current, the motion of the boat 

 with the whole suspended apparatus will have the same rate as that of the 

 simple float. 



39. Putting these respective cases conversely, it may be affirmed (1) that 

 if the boat, having the " current-drag " suspended from it, should move 

 with the surface-current and at the same rate, the stratum in which the 

 "drag" hangs may be presumed to have a motion nearly corresponding 

 with that of the surface-current ; (2) that if the rate of movement of the 

 boat with the surface- current should be retarded, a diminution of the rate 

 of the stratum in which the " drag " hangs, to a degree exceeding the retar- 

 dation of the movement of the boat, may be safely predicated ; (3) that 

 when this retardation is so considerable that the boat moves very slowly 

 in the direction of the surface-current, it may be inferred that the stratum 

 in which the "drag" is suspended is either stationary or has a slow move- 

 ment in the opposite direction ; (4) that if the boat should remain sta- 

 tionary, a force must be acting on the " drag " which is equal and in the 

 contrary direction to that of the upper current upon the boat and suspend- 

 ing line ; so that the existence of a counter-current is indicated, having a 

 rate as much less than that of the surface-current, as the resisting surface 

 presented by the " drag " is greater than that offered by the boat and 

 upper part of the suspending line ; (5) that if the boat should move in a 

 direction opposed to that of the surface-current, a motion is indicated in 

 the stratum in which the "drag" hangs which will correspond in direc- 

 tion with that of the boat, and which will exceed it in rate, the effect of 

 the " drag " upon the boat being partly neutralized by the antagonistic 

 drift of the surface-current. 



40. Now our first set of experiments (Station 39) with the " current- 

 drag" gave the following results: — 



I. The surface-movement being first tested in the manner already de- 

 scribed (§ 36), its rate was found to be 2*88 nautical miles per hour, and 

 its direction E. by S. f S. The wind was W. by N., with a force of 4. 



II. The " drag " having been lowered down to a depth of 100 fathoms, 

 the rate of movement of the boat from which it was suspended was reduced 

 to 1*550 mile per hour, or rather more than half the surface-movement. 

 Its direction was E. 5 S. Taking into account the action of the wind and 

 surface-current on the boat, it may be safely affirmed that at 100 fathoms 

 the rate of the current was reduced to less than one half. 



