About once a month, according to Hensen, the Baltic is
of such low specific gravity that the plaice eggs sink;
and the inference is that their development is thereby per-
manently checked, since floating eggs are not adapted to
healthy development at the bottom of the sea. The extra-
ordinarily low percentage of salt in that sea can hardly be
appreciated by those who have neither bathed nor fished in
it; but the writer well remembers, though twelve years have
elapsed since he resided on its shores, the comparative difficulty
of keeping afloat on its surface for one accustomed to sea-
bathing in the Channel and Mediterranean, and also the
curious sensation of catching, a mile or two from shore,
such a medley of sea- and river-fish as plaice, pike, perch,
and cod, not necessarily on the same ground, but within an
area of probably less than an acre. The low percentage of
salt is not difficult to account for in a sea that, having no
outlet save the narrow strait that connects it with the North
Sea, receives so many torrential waters from the melting
snows of southern Scandinavia, besides so many slower yet
broader streams from the lowlands of northern Russia and
Germany. The curious variations in the salinity, however,
have yet to be satisfactorily understood.
