for evaporation less than it does over the Atlantic; and thirdly,
supposing these two questions answered affirmatively: Are not these
sources of loss in the Mediterranean fully covered by the prodigious
quantity of fresh water which is poured into it by great rivers and
submarine springs? Consider that the water of the Ebro, the Rhine, the
Po, the Danube, the Don, the Dnieper, and the Nile, all flow directly or
indirectly into the Mediterranean; that the volume of fresh water which
they pour into it is so enormous that fresh water may sometimes be baled
up from the surface of the sea off the Delta of the Nile, while the land
is not yet in sight; that the water of the Black Sea is half fresh, and
that a current of three or four miles an hour constantly streams from it
Mediterraneanwards through the Bosphorus;--consider, in addition, that no
fewer than ten submarine springs of fresh water are known to burst up in
the Mediterranean, some of them so large that Admiral Smyth calls them
"subterranean rivers of amazing volume and force"; and it would seem, on
the face of the matter, that the sun must have enough to do to keep the
level of the Mediterranean down; and that, possibly, we may have to seek
for the cause of the small superiority in saline contents of the
Mediterranean water in some condition other than solar evaporation.

Again, if the Gibraltar indraught is the effect of evaporation, why does
it go on in winter as well as in summer?

All these are questions more easily asked than answered; but they must be
answered before we can accept the Gibraltar stream as an example of a
current produced by indraught with any comfort.

The Mediterranean is not included in the _Challenger's_ route, but she
will visit one of the most promising and little explored of
hydrographical regions--the North Pacific, between Polynesia and the