124 
THE FRESH-WATER LOCHS OF SCOTLAND 
the left represents a return current in the opposite direction to 
the wind. 
Observation in Loch Ness was difficult for various reasons, but 
measurements made in the spring of the year showed very slow 
currents at depths of from 500 to 600 feet. Numerous observations 
were also made in Loch Ness after the discontinuity had appeared, 
and although the results obtained were extremely complicated, it 
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appeared that the return current took place above the discontinuity, 
sometimes very near the surface. It also appeared that the return 
current was nearer the surface at the windward than at the lee end 
of the lake, which is natural, as it might be expected that they would 
follow the direction of the isotherms (see fig. 47). 
Below the discontinuity the currents were during the autumn so 
slow that they could scarcely be detected by means of the current- 
meter, but as winter progressed they became appreciable to greater 
and greater depths. 
An investigation of the circulation in lakes is important from the 
