394 Proceedings of Royal Society of Edinburgh. [sess. 
■ 4 Taman.” I began to take observations of the specific gravity of 
the water at different depths, and I found out that the water form- 
ing tbe lower strata contained twice as much salt as the water of 
the upper strata ; after this a double current was quite evident to me. 
In order to measure tbe velocity of both currents, I invented tbe 
instrument wbicli is shown on Plate II. It consists of a pro- 
peller revolving on a horizontal spindle. A bell is attached to the 
propeller, the tongue of which is arranged to move on an axle in 
one direction ; at every revolution of the propeller it strikes twice, 
and, as water is a very good conductor of sound, the number of 
revolutions could be counted through the bottom of the ship (pro- 
vided the ship is not sheathed with wood) at all depths to which 
the instrument was lowered (40 fathoms). To this instrument I gave 
the name of fluctometer, and I used it during the whole year, lower- 
ing it on a wire rope with ballast of 80 lbs. of lead attached below. 
Plate I. fig. 2 shows the velocity of both currents in feet per 
second, and the specific gravity of the water in each stratum. 
Observations were made every two hours, and the specific gravity 
of water from every depth was taken at the same time when the 
velocity of the current was observed. 
I do not wish to keep you long with the different interesting 
details, and will only point out to you that the lower current is 
similar in many details to an ordinary river, while, on the contrary, 
the upper current differs much from an ordinary river, probably 
from the reason that, while the surface of it is falling gradually 
down, the bottom rises constantly (see Plate I. fig. 1). 
The difference of level of the Black Sea and Marmora Sea 
calculated from the difference in the specific gravity of the water 
I found for the month of July 1882 to be 1*396 feet. 
In the Strait of Gibraltar I had only five stations, and made my 
observations one day only. I had no opportunity of measuring the 
velocity of the current, but the phenomenon is very similar to what 
I found in the Bosphorus. Plate III. shows a section of the Gib- 
raltar Strait and the Mediterranean as far as the Syrian coast. Of 
course, the Mediterranean is given in a different longitudinal scale 
from that of Gibraltar Strait. As shown by the diagram, the water 
of the Atlantic rushes into the Mediterranean, the difference between 
the surface levels being, according to my calculations, 0'54 feet. 
