RECENT HYDROBIOLOGICAL INVESTIGATIONS 483 



the middle of the line is much denser. As a rule the water 

 near the sea-bottom is both colder and denser than that at 

 or near to the surface. In the open sea off the coasts of 

 Britain and Norway practically all the water at or beneath 

 the surface will have a salinity of over 35 per thousand : in 

 any hydrographic section, then, the proportion of the whole 

 area covered with water of this salinity measures directly the 

 strength of the Gulf Stream drift. 



It would be possible to measure the area beneath the lines 

 of observation filled with truly Atlantic water, and then, by 

 measuring the velocity of the drift and ascertaining the mean 

 temperature, to find the quantity of heat conveyed per unit 

 of time into any of these northern regions of sea. But the 

 velocity of the drift is not exactly known, and such a calculation 

 would, in the meantime, be a very rough one. It is sufficient 

 to take such a section as that running out from Sognefjord, 

 the more southerly of the two Norwegian lines shown on 

 the chart (fig. 1), and to estimate the area of the section con- 

 taining water of over 35 per mille. salinity, and multiply this 

 value by the temperature. Relative measures of the amount 

 of heat transported by the drift are so obtained, and these 

 values are also measures of the strength of the Norwegian 

 Stream ; or, more precisely, they are functions of both this 

 and the strength of the East-Icelandic Polar Stream, supposing 

 that the latter were a factor in the year considered. Now the 

 study of the Sognefjord line of observations in this manner 

 gives the following series of values : 1 



Product of the sectional area, beneath the Sognefjord line, filled with 

 zvater of 35 per mille, salinity or over, into the mean temperature. 



Thus there are significant variations in the figures so obtained 

 in this series of years. 



1 Nansen and Helland-Hansen, "Die jahrlichen Schwankungen der Wasser- 

 massen im Norvvegischen Nordmeer ihrer Beziehung zudem Schwankungen der 

 Meteorologische Verhaltnisse, der Ernteertrage und der Fischereiergebnisse in 

 Norwegen," Internal. Revue Gesamt. Hydrobiologie und Hydrographic, Bd. ii., 

 Nr. 3, 1909, pp. 337-61. 



