— 62 — 



0,5 "/[IQ. Only in the coastal regions, when the admixture of fresh water from 

 the land is most noticeable, is the mean amplitude of the surface salinity 

 greater, being in the inner part of the German Bight at Heligoland greater 

 than 5 "/qq and at the surface of the Skagerak several times greater still. 

 The times at which highest and lowest salinity occur appear to vary consider- 

 ably from place to place, and can only be roughly characterised as a general 

 tendency towards high salinity in winter and low in summer; at certain 

 places there seem to be very distinct exceptions to this rule. 



As regards occasional variations, the main rule applies, that they are 

 small in the salt oceanic water in the Scottish regions, and greater in the 

 landward zones where the coastal water makes itself felt. Thus during the 

 first half of June 1911, the salinity at Lat. 58° 28' N— Long. 0° 12' W. did 

 not vary at any depth more than 0,06 "/po, while at m. it was 10,8 "/„o at 

 57°33',5 N— 8°24',5 E, and 7,98 »/„o at 57°55' N— 4°45' E. 



b. Temperature. 



In the southern part of the North Sea, south of 54° N and west of 

 5° E, the water column at each separate place has at all times of the year 

 very nearly the same temperature from surface to bottom, and the same is 

 true of the Channel east of 2° W. In this region the mean difference of 

 temperature between surface and bottom does not at any time of the year 

 exceed 0,6°, and is as a rule considerably less. In winter the same rule 

 applies for the water in the greater part of the North Sea, south of the 

 100 m. Isobath, there being here nearly everywhere a mean difference of 

 temperature between surface and bottom of less than 1/2°. It is otherwise, 

 however, in summer, when the region north of the Dogger Bank, — consider- 

 ably less than 100 m. deep — shows, on an average, a difference in tempera- 

 ture of 7 — 8° between the uppermost and lowest water layers. 



In winter the temperature of the water increases from the coasts out- 

 wards to the open sea, the reverse being the case in summer. In February 

 the lowest mean temperature (abt. 3°) is found at the surface along the 

 Dutch and Danish coasts; in the middle of the North Sea the average tem- 

 perature is abt. 6°, in the Straits between Dover and Calais 7° and in the 

 western part of the Channel abt. 10°. In parts of the Skagerak and the 

 Norwegian Channel over 100 m. deep,^the warmest water (from 6^/2° to over 

 7°) is not found at the bottom, but in the intermediate layers, at depths 

 varying from 100 to 300 m.; ^at the [bottom the temperature lies between 

 51/2° and 6^/2°, at the surface, however, between 3° and 4° in the inner part 

 of the Skagerak and abt. 5° in the Norwegian Channel. In August the warm- 



