1872.] 



' Shearwater 1 Scientific Researches. 



641 



decrease in the movement of the "current-buoy," from 2| knots at the 

 surface to almost nothing at 20 fathoms, indicates (as just now shown) 

 first a cessation of all movement in the stratum in which the " current- 

 drag " hangs, and then a reversal in the direction of the current as the 

 lower depth is approached, — the Specific Gravity was found to increase 

 from 1020 at the surface to 1028 at 20 fathoms and 1029 at 40 fathoms ; 

 the surface-water thus corresponding with that of the Sea of Marmora, 

 whilst the water of the entire stratum from 20 fathoms to the bottom was 

 equal in density to that of the Mediterranean. 



173. I hold, then, that the existence of an Under-current of dense 

 Mediterranean water through the Dardanelles into the Sea of Marmora is 

 incontestable proved by the very experiments and observations which have 

 been adduced by Capt. Spratt as demonstrating the unsoundness of the 

 Under-current doctrine *. 



[Addendum (Oct. 21, 1872). — Information has just reached this 

 country, through the ' Levant Herald/ that the investigation of the Dar- 

 danelles Current made by the Surveying Staff of the ' Shearwater ' since 

 the above paragraphs were written on board her, has confirmed my original 

 prediction, and entirely justified my interpretation of Captain Spratt's experi- 

 ments. For, according to the statement of this journal (obviously made on 

 authority), a boat was carried along by a " current-drag " suspended in the 

 Under-current, in opposition to the surface- current, at a rate greater than 

 the speed of the 'Shearwater's' steam-launch; and this under-current 

 has been ascertained to run at a depth of 20 fathoms, — precisely that 

 at which the results of Captain Spratt's experiments led me to predicate 

 its existence. ] 



I venture to think that this complete verification of my prediction will 

 be regarded as a confirmation of the general Physical Theory of Under- 

 currents on which it was based : and it is now incumbent on those who 

 oppose that Theory, to show by what other force than the difference in 

 the weight of the iEgean and Black Sea columns, arising from their great 

 difference in Specific Gravity, the Dardanelles Under-current can be sus- 

 tained. 



That a similar Under-current exists in the Bosphorus, has been (as I 

 am assured by my friend Mr. Redhouse, who resided many years at Con- 

 s tantinople as Translator to the British Embassy) long known to the native 



* It furnishes no argument against this conclusion, that (as stated by Capt. Spratt) 

 during the winter months, when the Black-Sea rivers are at their lowest, a return 

 siirface-cm'rent is propelled into it by Westerly winds, from the iEgean, through the 

 Dardanelles, Sea of Marmora, and Bosphorus. For the direction of the surface-current 

 is entirely a question of Wind and of relative level ; and the occasional reversal of that 

 direction does not prove the non-existence of an inward wwefcr-current sustained by 

 difference of vertical pressure. How a surface wind-current can bring into the Sea of 

 Marmora the deep stratum of JEgean water which is proved by Captain Spratt's own 

 Specific Gravity observations to overlie its bottom, he docs not explain. 



