1872.] 



1 Shearwater' 3 Scientific Researches. 



5G9 



surface-stvditwm was found to be moving eastwards at the rate of 1*7 

 mile an hour ; 3£ hours later, the direction was still the same, but the 

 rate had diminished to 1*5 mile an hour ; 2 hours after Low water, when 

 the tide was rising, the surface- current was moving to the westward at the 

 rate of 1 mile per hour ; and at 4-5 hours after Low water, its direction 

 being still the same, its rate of movement had fallen to 0*4 mile per hour. 

 In the earlier part of the day, the under-cxment at 150 fathoms was found 

 to be moving to the eastward, but an accident prevented the determination 

 of its rate. In the afternoon, however, 2 hours after Low water, a current- 

 drag suspended at a depth of 1 25 fathoms moved westward at a rate of 

 1*35 mile an hour ; which, allowance being made for the resistance to the 

 motion of the surface-buoy, was considered by Capt. Nares to indicate that 

 the rate of westward flow of the under-current was really 1*5 mile per 

 hour, exceeding that of the surface-movement in the same direction by 

 0*5 mile. 



52. On the following day we took up our position on the north part of 

 the "ridge" between Capes Spartel and Trafalgar, over a bottom of 125 

 fathoms depth. The weather being very calm, and the water smooth, 

 every thing was favourable to the prosecution of our inquiries. The Specific 

 Gravity of the surface-water being 1*0271, and that of the bottom-water 

 1029*2, the presumption was very strong that, while the upper stratum 

 consisted of Atlantic water, the lower stratum consisted of Mediterranean 

 water ; and the first question to be determined was the depth of each. "We 

 found that at 50 fathoms the Sp. Gr. had increased to 1*0273, and that at 

 100 fathoms the Sp. Gr. showed a further increase to 1*0276 ; but that a 

 marked increase from this to 1*0290 showed itself before the depth of 110 

 fathoms was reached ; so that while the lower part of the Atlantic stratum 

 showed a sufficient admixture of Mediterranean water to affect very sen- 

 sibly its Specific Gravity, the stratum below 110 fathoms might be con- 

 sidered as consisting essentially of Mediterranean water. 



53. The experiments with the Current-drag were commenced at 2\ 

 hours after High water, when the ebb-tide was running eastwards. The 

 current on the surface was running inwards at the rate of 1*25 mile per 

 hour; and this was also found to be its rate at 25 fathoms depth. When 

 the drag, suspended from a small boat, was lowered to 100 fathoms, it still 

 moved to the eastward, but at a slower rate ; the surface-current passing 

 the boat at the (estimated) rate of 0*25 mile per hour. The drag being 

 then lowered to 1 1 9 fathoms, and suspended from a buoy, it first moved 

 eastwards at the rate of 0*18 mile per hour ; and then at Low water, while 

 the surface-cuvvewt was still moving east, it began to move ureftwardSj 

 retarded at first by the action of the surface-current on the floating buoy. 

 At 1 hour after Low water, the surface-current having stopped running, 

 the current-drag had drifted 0*18 mile to the west ; but as it was found 

 then to have grounded in 118 fathoms, its line was shortened to 108 

 fathoms. It immediately ran away with its buoy to the westward, drag- 



