536 



Captain Spratt on the Undercurrent 



[June 15, 



of the operation too, especially when testing any very slow ocean-current, 

 of only O'l of a mile per hour or less, which is quite practicable, as I have 

 frequently done. And it is rendered sure and easy by always having a fixed 

 float with sinker at the bottom as a point of reference, even where objects 

 are near and charts are correct, and also by using very fine twine as a log- 

 line to each float, and allowing it to run out from five to ten times the 

 usual interval in measuring a ship's rate. The diagram on p. 537 will 

 illustrate the matter*. 



The diagram referred to will illustrate the plan, and the result will 

 be more comprehensible and satisfactory, because sooner completed, if we 

 suppose the trials to have been made from two or three boats (instead of from 

 only one boat), each being provided with one or two buoys and suspended 

 sinkers to suit, and with lines to each arranged for different depths ; and if also 

 a fine log-line is attached to each float for measuring the distance it drifts 

 in a given time, and from it the rate of each float, the boats being always 

 kept abreast of each other. For although each float, from the different 

 times each suspended sinker will take to reach its intended depth, will have 

 drifted away to some small varying distance from the boats and stationary 

 float, these varying intervals will correspond to the stray line paid out in 

 measuring a ship's rate through the water ; and being noted in the usual way 

 (as the rate-lines will be duly marked at intervals of 10 feet), or by a piece 

 of cork or rag attached to each, when at the given signal the interval, 

 by watch or glass, is simultaneously commenced to be noted, the deduc- 

 tion of this stray portion from the whole length run out in the arranged 

 interval of five or ten minutes or more, according to the speed of the cur- 

 rent, will give the surface-rate of each, and the consequent rates of the 

 currents in which the suspended sinkers are lowered are easily deduced 

 from them. 



Now all these observations showed no undercurrent into the Black Sea, 

 such as Dr. Carpenter maintains must necessarily exist to restore the saline 

 density of that sea ; if, therefore, I can show how that density is otherwise 

 maintained, and by a more natural and more universal process and influ- 

 ence in connexion with ocean movements in all seas, the theory of universal 

 undercurrents, as a great circulating medium for recovering the equilibrium, 

 is deprived of its main support, — the main ground upon which it is advo- 

 cated as a predicted necessity. 



To better understand the remarks and facts that will follow upon the 

 densities and currents of the Black Sea Straits, I must briefly notice the 

 physical features influencing them. 



First, the Black Sea attains a depth of about 1000 fathoms and more 

 over a large portion of its area. The Sea of Marmora attains between 

 400 and 500 fathoms, and the iEgean about the same ; whilst the Darda- 

 nelles and Bosphorus do not exceed 20 and 40 fathoms. 



The facts, then, are simply that, although a diluted current of Black Sea 

 * Crete, vol. ii. Appendix, p. 338. 



