that of other seas, I cannot help thinking that there* 
must exist a contrary current under the upper one of 
the channel, which conveys the water of the sea of 
Marmara towards the Black Sea. Without this sup. 
position it would be impossible to explain how, during 
so many ages, the Black Sea has been able to preserve 
its saline quality, notwithstanding the enormous quantity 
of fresh water which it receives daily from the rivers, 
and the mass of salt water which runs from it by the 
Bosphorus. 
The balance necessarily produced by the different 
specific gravity of two bodies of water diversely charg- 
ed with salt, and which communicate with each other, 
concurs likewise to prove the necessity of the existence 
of this lower current from the Sea of Marmara towards 
the Black Sea; since if we suppose two perpendicular 
columns of water of the same height in the two seas, 
which can communicate by the channel, it is indubita- 
ble that that of the Black Sea, composed of salt water 
and the fresh water of rivers, must be lighter than that 
of the Sea of Marmara, which is composed almost en- 
tirely of salt water: consequently the Sea of Marmara, 
to adjust its weight with that of the Black Sea, ought 
to empty into the latter a part of its water, until the fall 
of its level, and the exhaustion of that of the Black Sea 
compensate the difference of the specific gravity of the 
two waters. Again, the prolonged column of the Black 
Sea not being able to support itself above the level of 
the corresponding column, will pour upon it a part of 
its superior water, to keep in equilibrium the level of 
the two columns, and thus is the superior current es- 
tablished from the Black Sea to that of Marmara, and 
kept up by the continual influx of the rivers which 
empty themselves into the former. The necessity of the 
