624 Proceedings of the Royal Society of Edinburgh. [Sess. 
100, 150, and 200 feet show a well-marked, if somewhat irregular, tempera- 
ture seiche. The rapidity of the change of temperature from 2nd to 3rd 
September is especially notable, and will be referred to later. 
Before proceeding to discuss the current observations it is necessary to 
point out that very considerable currents must accompany the temperature 
seiche, apart from the currents and return currents produced by winds. A 
AUGUST 1908 SEPTEMBER 
INVERNORISTON - LOCH NESS 
Fig. 3. 
rough calculation of the magnitude of these currents has been made as 
follows : — 
The mean depth of Loch Ness is about 138 metres (450 feet), and it was 
assumed that for the purposes of calculation the lake could be replaced by 
a rectangular basin of this depth and with a length of 36 km. (22J miles). 
It was further assumed that there was a sharply defined discontinuity at a 
depth of 46 metres (150 feet). Then for a seiche with an amplitude of 46 
metres the quantity of water both in the upper and in the lower layer trans- 
