1871.] 



Theory of the Ocean. 



553 



" The following is the mode practised : the surface-current was first 

 tried by the usual mode (a heavy iron kettle being lowered from a boat to 

 the depth of 80 fathoms), then for the trial of the undercurrent a large 

 chip-log, of the usual quadrantal form, the arc of it measuring full 4 feet, 

 and heavily loaded with lead to make it sink and keep upright, was lowered 

 by a light but strong cod-line to the depth of 126 fathoms (the length of 

 the line) ; a barrega was attached as a float, a log-line fastened to this 

 barrega, and the rate of motion to this float, as measured by this log-line 

 and the glass, and the direction as shown by a compass, were assumed as 

 the velocity and set of the undercurrent. No allowance was made for the 

 drag of the barrega, which ivas always in a different direction from the 

 surface-current. It was wonderful, indeed, to see this barrega move off 

 against wind and sea and surface- current at the rate of over one knot an 

 hour, as was generally the case, and on one occasion as much as If knot. 

 The men in the boat could not repress exclamations of surprise, for it 

 really appeared as if some monster of the deep had hold of the weight 

 below, and was walking off with it." 



It is therefore quite evident that Capt. Maury adopted Lieut. Walsh's 

 identical words and views as the sound solution of the experiments, viz. 

 that a great oceanic undercurrent circulation existed as a counterpoise to 

 the disturbed densities arising from temperature and salinity. 



Lieut. Walsh next cites from the log several instances of the experi- 

 ments, viz. at six positions in the Atlantic, between 24° 43' North and 

 65° 2' West, and 33° 58' North and 72° West, in which the weighted chip- 

 log was lowered to 126 fathoms in each position, to test the undercurrent 

 at that depth, as erroneously supposed. But in fact it was merely giving 

 a more correct indication of the surface-current than that resulting from the 

 iron kettle in 80 fathoms, with a large boat as its float, under the erroneous 

 impression that the iron kettle would be in still water at that depth, and 

 that it would retain the boat stationary as if anchored to the bottom ; 

 this, too, against wind and sea. It is, however, evident that the kettle-and- 

 boat experiment could only show a vitiated result, a diminished surface- 

 current to that actually existing. 



The kettle- and-boat experiment were only used once, however, at the 

 last position, in connexion with the large chip-log lowered down to 126 

 fathoms, which Lieut. Walsh regrets, by saying, " which it would have 

 been better to have always done." 



Now it must be quite evident from what I have before shown, from my 

 experiments for testing surface and undercurrents, or from the diagram 

 referred to, p. 537, how the rate of descending surface-currents, and of any 

 undercurrent, can be correctly ascertained, if existing as an appreciable 

 fact, although Lieut. Walsh did not then know " of any means of doing 

 so correctly ; " that, therefore, the float to the large 4-feet diameter chip- 

 log, lowered down to 126 fathoms, would naturally appear to run to 

 windward of the heavy boat attached to the iron kettle of less dimensions 



