HYDROGR. SECTION — APPENDIX D (54) 
Complete knowledge of the movement of the surface-water has been ob- 
tained at certain places mainly through observations on lightvessels and this is to 
a certain degree true of the deeper layers also in at least one place in the open 
sea, this result having been obtained by direct current measurements. 
Certain phenomena suggest that the water masses in the southern part of 
the North Sea to a certain degree belong to a region by itself with distinct hydro- 
graphic conditions. 
The exact knowledge of the conditions of the currents is of great impor- 
tance for the study of the fate of pelagic fish-eggs. 
A branch of the Atlantic current spreads over the northern North Sea 
plateau, running from the sea north of Shetland in a southerly and south-easterly 
direction. This current which is influenced by the configuration of the bottom, 
carries salt water partly into the central area of the northern North Sea plateau 
(more than 80 m. deep), partly along the western slope of the Norwegian Channel 
into the deeper parts of the Skager Rak. Giving off heat to the air during the 
winter this water is cooled down to a relatively low temperature, which is retained 
during the summer, the water in question then being the bottom-layer. The upper 
water-layers are renewed by new water masses which together with the coastal 
waters off Scotland and Norway produce a cyclonic circulation on the northern 
North Sea plateau, this fact being proved by the hydrographical conditions and. 
also by experiments with drifting bottles. 
North of the Dogger Bank there is a region in which the cold bottom water 
is, from a hydrographic point of view, somewhat different from the surrounding 
water. The coastal waters in the western as well as in the southern part of the 
North Sea acquire a special character from the strong tidal currents which act so as 
to render the water practically homogeneous from the surface to a considerable depth. 
It has become obvious that the unperiodic variations in the North Sea are 
of very great importance. The variations take place with very varying rapidity. 
The conditions may also be very different from year to year. Thus the Atlantic 
water obtained a much greater extension in 1905 than in previous years, both 
temperature and salinity having unusually high values in 1905 not only in the 
Atlantic Ocean and in the Channel but also in the North Sea. 
V. Channel: 
The. tidal currents of the English Channel exercise a profound influence 
especially in the northeastern part. The water in the Channel comes from the 
Atlantic Ocean but it is often strongly influenced by the water of the Bay of 
Biscay or by that of the Irish Sea. These changing currents produce changing 
