640 



Dr. W. B. Carpenter on the 



[June 13, 



in toto as to the cause of its stationary condition : for whilst he concludes 

 that the current-drag remains stationary because it hangs in perfectly 

 still water, it appears to me beyond question that it can only remain 

 stationary whilst acted on by a current flowing in the opposite direction. 



170. For let us consider (1) the condition of the "anchored buoy" 

 lying in a surface- current that runs at the rate of (say) a mile per hour. 

 The resistance offered to that current, not only by the buoy, but by the 

 upper part of the anchoring line, puts that line on the stretch, so as to 

 bring a very considerable strain alike on the buoy and on the sinker at the 

 bottom. — In our own experiments in the Strait of Gibraltar, this strain was 

 found to be so great, that a current of 1*25 mile per hour was sufficient to 

 submerge a buoy capable of floating a weight of 100 lbs.; and when 

 another buoy was attached to this, so as to keep it up to the surface, the 

 strain of the current on the two proved so great as to lift and displace 

 the sinker at the bottom, though it was a "mass of iron weighing 1 cwt. 

 — Let us suppose (2) the "current-drag "to be freely suspended in per- 

 fectly-still ivater, at any depth whatever above the bottom ; it is obvious 

 that, as the pressure of the surface-current upon its buoy and suspending 

 line is precisely the same as in the preceding case, such pressure will put 

 a strain upon the line, which will draw the " current-drag " along through 

 the still water, in the direction of the surface-current, but at a reduced 

 rate * ; the flow of the current past the " current-buoy " being diminished 

 by the amount of that motion. 



171. Now if this be admitted, it necessarily follows (3) that if a "cur- 

 rent-drag" suspended from a buoy floating in a surface-current remains 

 motionless, — as shown by the equality of the rates of flow of the surface- 

 current past the "current-buoy" and the "anchored buoy," — the strain 

 put upon its suspending line by the resistance of its current-buoy to the 

 surface-current must be neutralized by the pressure in an opposite direction 

 of an Under-current meeting the " current-drag." 



172. And since, according to Capt. Spratt, this stationary condition of 

 the "cur rent- drag" was shown at all depths below 40 fathoms in the Sea of 

 Marmora (even down to 400 fathoms), and at all depths below 20 fathoms 

 in the Dardanelles, whilst there is a rapid superficial out-current, running 

 in the Dardanelles at the rate of 2\ miles per hour, it seems an irresistible 

 conclusion that there is a deeper Under-current from 20 fathoms to the 

 bottom, running more slowly Awards from the iEgean into the Sea of 

 Marmora through the Dardanelles, and thence (it may be presumed) 

 through the Bosphorus into the Black Sea. And this conclusion finds 

 complete confirmation in the results of a comparison between the respective 

 densities and rates of movement of the Dardanelles water at different 

 depths, as observed by Capt. Spratt himself. For whilst the progressive 



* It is not a little singular that Capt. Spratt admits this action (p. 535) in a case in 

 which the " current-buoy " continued to move with the surface-current at the rate of 

 0*1 knot per hour; whilst refusing to admit it when the " current-buoy " was stationary. 



