1908-9.] Observations with a Current Meter in Loch Ness. 629 
The loch was nearly calm on the evening of the 17th, but the wind rose 
again the next day, and north-easterly currents of 112 cm. sec. at the surface, 
8 cm. sec. at 30 feet, 3*5 cm. sec. at 80 feet, and 7*4 cm. sec. at 90 feet, were 
observed. The directions at 90 feet were not, however, very consistent, and 
at 96 feet a southerly current of 1 cm. sec. was observed, and at 102 feet 
a N.W. current of 1*6 cm. sec. 
The general conclusions to be drawn from these observations during N.E. 
winds would seem to be that at the station of observation, i.e. near the lee 
end of the lake, for moderate winds the return current confines itself to the 
deeper water and takes place in the neighbourhood of the temperature discon- 
tinuity. The return current seldom penetrates to the cold water below the 
discontinuity. The effect of very strong winds can only be guessed at, as 
observation was impossible with the boats and apparatus at our disposal. 
On one occasion the meter happened to be suspended at 180 feet from 
the buoy during a strong N.E. wind, viz. on 1st September, when a N.E. 
gale was sandwiched between two days of calm. The overnight observa- 
tion showed a slow current (1 cm. sec.) with variable direction. (There were 
thirteen balls indicating direction, and while one was in the N.E. quadrant the 
remaining twelve were equally distributed over the other three quadrants.) 
This isolated observation is not inconsistent with the above conclusion. It 
should, however, be mentioned that although the return current does not 
appear to descend below the discontinuity, direct currents do appear to 
penetrate to considerable depths at the commencement of the north-east 
winds, and only after the wind has continued for some time does the return 
current displace the direct current and force it to be confined to a less depth. 
An examination of the results of south-westerly winds does not appear to 
give the same conclusions, but they are not inconsistent therewith. The 
general rule is that strong return currents are met with very near the surface, 
no matter what is the strength of the wind. This may be due either to the 
fact that the observation station was near the windward end of the lake, 
or to the sheltered position of the buoy. The position was slightly sheltered 
by Portclair Point, which forms the western side of Invermoriston Bay. 
It was more than once suggested that the return current might be felt very 
deep on the exposed side of the station, and that Portclair Point caused 
subsidiary return currents near the surface. Whatever the cause, there is 
not the same consistency about the results during S.W. winds as during 
N.E. winds. But it is clear, especially with strong winds, that the return 
current at the point of observation took place near the surface (cp. observa- 
tions on 27th and 28th August). With a S.W. wind succeeding a day of 
calm or N.E. winds, S.W. currents are set up at considerable depths — e.g., at 
