TEMPERATURE OF THE HYDROSPHERE 191 



on the surface and from 14° to nearly 16° at the bottom. Below 

 this surface layer a sudden drop occurs, a feature characteristic of 

 fresh-water lakes. Thus east of Rornholm observations by F. L. 

 Ekman in July, 1877, showed a surface temperature of 15.7° C. 

 slowly decreasing to 14° at 18 meters depth, followed by a sudden 

 drop to 8° at 20 meters, decreasing regularly to 5° at 25 meters. 

 The salinity here was 7.5 permille down to 30 meters, where it rose 

 to 7.6 permille. Such abrupt changes are found only in water 

 bodies of slight wave and current activities. 



So far as measurements have been made in Hudson Bay, a nearly 

 homothermal condition seems to be indicated, with temperatures 

 between — 0.3° and — 1.7°, to a depth of 365 m. The North Sea 

 is a typical and well-studied example of a marginal epicontinental 

 sea. Southwest of the Dogger bank the strong wave activity and 

 tides produce a homothermal arrangement which in winter has a 

 temperature of 5° to 6°. Northward and eastward this decreases to 

 4° or even 3°. After a period of quiet days a surface layer of less 

 salinity may form from the influx of fresh waters, and with this a 

 low temperature occurs. Thus, while the salinity of the surface at 

 the German station 15 (lat. 55° 2' N., long. 7° 30' E.) fell to 32.5 

 permille on February 24, 1906, the temperature fell to 2.89° ; both 

 salinity and temperature increased downward, being at 24 meters 

 32.18 permille and 3.20°, respectively. A typical kathothermal condi- 

 tion for February is shown by measurements off the mouth of the 

 Moray Firth (Scottish station 25, lat. 58° w' N., long. 0° 32' W.) 

 on February 18, 1904, when the temperature rose from 6.63° at the 

 surface to 6.77° at no m., and the salinity from 35.10 permille to 

 35.14 permille at the same depths. In the summer the reverse is 

 true, the surface temperature (18°) being slightly higher than the 

 bottom, 7.6°, at 35 m., except where after storms a homothermal 

 and homohaline condition prevails. A sharply defined stratification 

 may occur even here, as shown by observations in the open North 

 Sea in August, 1905 (lat. 55° 22' N., long. 4° 18' E.), when it 

 was found that the temperature decreased slowly from 15.74° on the 

 surface to 15.67° at 20 meters, then fell to 11.38° at 25 meters, and 

 to 8.26° at 30 meters, and 8.25° at 43 meters. On the west side of 

 the Great Fisher bank the observations for '1903 show a sudden drop 

 from 12.24° at 30 m. to 6.52° at 40 m., with but little decrease be- 

 low this. Such a condition is general north of the Dogger bank. 



Temperatures of Dependent Seas. In the Funnel seas with 

 closed head the conditions of the ocean to which they are dependent 

 prevail, and this is true of tlie Biscayan as well as of the California 

 type. Where the head is open, leading into a mediterranean, the 



