TEMPERATURE OF SCOTTISH LAKES 
123 
return current along the discontinuity surface has the same effect 
on the lower layer of water as the wind current has on the surface 
of the water, and in consequence the lower isotherms slope down- 
wards from the end of the lake from which the return current begins, 
that is, fi'om the lee end of the lake, and with a slope in a direction 
opposite to that of the upper layer, producing a fan-like arrangement. 
In consequence, the discontinuity always appears sharper at the lee 
end of the lake than at the windward end. 
During the year 1908 the author, along with Mr W. Watson, 
carried out some observations on the currents in Lochs Garry and 
Fig. 47. 
Ness by means of Ekman's propeller current-meter. The Loch 
Garry observations indicate clearly the existence of a return current 
reaching to the bottom of the lake. Fig. 48 is drawn from observa- 
tions made on 31st March, when the temperature of the water at the 
surface was 38° "7 Fahr., and at the bottom 38° '8 Fahr., and shows 
how the westerly current at the surface, caused directly by the action 
of a strong west wind, was felt to a depth of about 50 feet, and how 
below that depth there was an easterly current which within 20 feet 
of the bottom of the lake had a rate of 3 centimetres per second. 
The rate of the current is measured along the abscissa axis, the 
unit being centimetres per second. The depth of the current is 
measured along the ordinate axis, the units being feet. The portion 
of the current to the right of the zero line represents a westerly 
current, i.e. in the same direction as the wind. The portion to 
