DIVERSION OF THE NILE. 621 
the Don and the Volga; but these works, though not wanting 
in commercial and political interest, do not possess any geo- 
graphical importance. It is, however, very possible to pro- 
duce appreciable geographical changes in the basin of the Cas- 
pian by the diversion of the great rivers which flow from Central 
Russia. The surface of the Caspian is eighty-three feet below 
the level of the Sea of Azoff, and its depression has been ex- 
plained upon the hypothesis that the evaporation exceeds the 
supply derived, directly and indirectly, from precipitation, 
though able physicists now maintain that the sinking of this 
sea is due to a subsidence of its bottom from geological causes. 
At Tsaritsin, the Don, which empties into the Sea of Azoff, 
and the Volga, which pours into the Caspian, approach each 
other within ten miles. Near this point, by means of open or 
subterranean canals, the Don might be turned into the Volga, 
or the Volga into the Don. If we suppose the whole or a 
large proportion of the waters of the Don to be thus diverted 
from their natural outlet and sent down to the Caspian, the 
equilibrium between the evaporation from that sea and its 
supply of water might be restored, or its level even raised 
above its ancient limits. If the Volga were turned into the 
Sea of Azoft, the Caspian would be reduced in dimensions 
until the balance between loss and gain should be re-estab- 
lished, and it would occupy a much smaller area than at pres- 
ent. Such changes in the proportion of solid and fluid surface 
would have some climatic effects in the territory which drains 
into the Caspian, and on the other hand, the introduction of a 
greater quantity of fresh water into the Sea of Azoff would 
render that gulf less saline, affect the character and numbers 
of its fish, and perhaps be not wholly without sensible influence 
on the water of the Black Sea. 
Diversion of the Nile. 
Perhaps the most remarkable project of great physical 
change, proposed or threatened in earlier ages, is that of the 
