532 



Captain Spratt on the Undercurrent 



[June 15, 



current, and that was also easily affected by the resistance it offered to the 

 wind and swell, and consequently the counter drift resulting from them, and 

 thus necessarily tending to mask the more delicate movements in the deeps 

 and to vitiate the results. 



I felt, too, that a fixed object as a point of reference was always necessary, 

 such as a buoy or float attached to a sinker actually upon the bottom. 



Such observations for testing ocean-currents, then, should only be made 

 in connexion with a fixed object attached to the bottom, whether in 

 2000 fathoms or 20 fathoms, as I have before recommended both in the 

 * Nautical Magazine ' and in the Appendix to ' Researches in Crete/ when 

 treating on the question of undercurrents in the Dardanelles and iEgean, 

 &c, from which latter work I shall have to quote a few passages in proof 

 of the actual conditions existing there. I am therefore induced here to 

 express my regret that the same means were not adopted in the Straits of 

 Gibraltar, especially as two or three good opportunities offered when the 

 dredge had got irrecoverably entangled at the bottom. 



I now give the following extracts referring to the observations made in 

 the iEgean Sea, Dardanelles, Black Sea, &c, to test the rate and depth 

 of the current generally flowing from the latter into the former, as also the 

 different densities of these seas and straits ; and the results arrived at will 

 be seen to have a very interesting and important bearing upon the theory 

 and question at issue. 



The densities were tested by an hydrometer, which, having a range 

 from about 13g° as the normal condition of the surface of the Black Sea, 

 to 29° as the normal of the ^Egean and Mediterranean seas, served to show 

 the varying densities in different depths and localities between them with 

 sufficient accuracy, without need of more elaborate analysis, such as might 

 be necessary in the Straits of Gibraltar, where the difference is only about 



Having carried out these observations at different depths in the Sea of 

 Marmora and the Dardanelles, from below the Dardanelles Castles, a very 

 interesting fact was ascertained, — namely, that nearly in proportion as 

 the descending superficial current from the Black Sea diminished, so did 

 the saline density of the water increase ; and where there appeared to 

 be no current (that is, below 40 fathoms in the Sea of Marmora, and below 

 20 fathoms in the Dardanelles) the density remained the same at all 

 depths, and was that of the Mediterranean density. 



Thus, in the Sea of Marmora, the density of the water in 40 fathoms, 

 and from the bottom at 400 fathoms, was the same, viz. 29° by the 

 hydrometer, and about corresponded with my observations on the Me- 

 diterranean density in general down to 2000 fathoms, except in one instance, 

 Crete and Lybia, when it was 30° at that depth, and at another only 28 j 

 at the depth of 1200 fathoms, with 29J above*. 



Then in the Dardanelles the current was found to cease at 20 fathoms, 

 * See Crete, vol. ii. p. 332. 



