208 



Messrs. Carpenter and Jeffreys on 



[Dec. 8, 



the surface inflow ; and (2) to determine, by the Temperature, the Specific 

 Gravity, and the Composition of samples of water taken up at different 

 points and from different depths, whether they had been drawn from the 

 Atlantic or from the Mediterranean basin. — The mechanical method was 

 entirely devised and carried out, with the practical ability for which he is 

 eminently distinguished, by our excellent friend Staff- Captain Calver (see 

 § 37). The physical and chemical observations, which were made under 

 our own direction, gave results which harmonize completely with those of 

 the mechanical, where both could be employed together ; and supply a 

 deficiency which the impossibility of applying the mechanical test on the 

 uneven bottom of the shallow ridge would otherwise have left, in the proof 

 of the outflow of Mediterranean water over it. 



115. Our investigations were first made in the mid-stream between 

 Gibraltar and Ceuta, at nearly the narrowest part of the Strait, where its 

 depth exceeds 500, fathoms (Chart II. Section c d). The decided retarda- 

 tion of the boat by the " current-drag " at 100 fathoms in both sets of experi- 

 ments (§§ 40, 62) showed that the in-current at that depth has less than half 

 the velocity of the surface-current. When the " current-drag " was lowered 

 to 250 fathoms, there was in the First set of experiments simply a further 

 increase of retardation, the boat being kept almost in a stationary position : 

 we felt justified, however, in inferring that the strain of the " current-drag" 

 could not have so nearly neutralized the action not only of the surface- 

 current, but also of the wind, upon the boat from which it was suspended, 

 if it had not been itself acted on by a counter-current. And this view 

 derived very strong confirmation from the evidence afforded by the Tem- 

 perature, the Specific Gravity, and the Density of the water in the 250 

 fathoms' stratum. For, in the first place, the surface-temperature being 66°, 

 and the temperature at 1 00 fathoms having fallen to 55°'7, no further reduc- 

 tion showed itself below that stratum ; the water at 250 fathoms, like the 

 bottom-water at 5 1 7 fathoms, having exactly the same temperature as the 

 water at 1 00 fathoms. This, as we have seen, is the uniform rule in the Medi- 

 terranean, whilst far otherwise in the Atlantic. Further, the Specific Gravity 

 and the proportion of Salt in the water at 250 fathoms indicated a density 

 which no Atlantic water possesses, and which was not exceeded in any 

 sample obtained from the Mediterranean. There could be no question, 

 therefore, that the stratum at 250 fathoms must be Mediterranean water ; 

 so that, if not absolutely stationary, it must be moving westwards. Now 

 this westerly movement was distinctly demonstrated in our Second set of 

 experiments, by the motion of the boat from which the "current-drag" 

 was suspended (§ G2) ; and since the observations on the Temperature, 

 Specific Gravity, and Salinity of the water in this stratum, which were 

 then repeated, gave results almost precisely identical with those made on 

 the previous occasion, it seems fair to conclude that there was a westerly 

 current in this stratum in the First, as well as in the Second instance, 

 though its effect on the current-drag was masked by the stronger antago- 



