132 THE FRESH- WATER LOCHS OF SCOTLAND 
the work of Thoulet, but it is strange that a period of ten years 
should have elapsed before any further remark was made on the 
temperature oscillations in lakes. 
Abysmal Temperatures 
At the bottom of the deepest of our lakes there is a body of 
water which varies little in temperature from one year's end to another, 
and the temperature of this abysmal layer depends largely on the 
temperature of the preceding winter ; but the wind-storms during 
the year also have a considerable effect in determining abysmal 
temperatures. In winter all the water in the lake becomes of a 
uniform temperature, and it is about this temperature that the water 
at the bottom of the lake remains during the ensuing summer. But 
the abysmal temperature is not quite constant. Thus, in Loch Morar 
at 1010 feet, on 29th March 1903, a temperature of 41° -8 Fahr. was 
observed ; while at a depth of 1000 feet, on 23rd October the tempera- 
ture was 43° '0 Fahr., showing an increase of as much as 1°2 Fahr. during 
the year. There is not always so great an increase ; thus, in 1887 
a number of serial temperatures were taken by Sir John Murray 
which show a practically constant temperature of 42°*0 Fahr. at 
great depths throughout the whole year. In Loch Ness, however, 
the range at a depth of 700 feet both in 1903 and 1904 was from 
41° -3 to 42° -6 Fahr.— a range of l°-3. In Loch Katrine, with a 
maximum depth of 495 feet, the range of temperature at the bottom 
is from 3 to 4 degrees. In Loch Garry (Ness basin), with a depth of 
213 feet, the range in 1908 was about 10° Fahr.— from 37°-5 to 47°-0. 
Sir John Murray has pointed out the influence of winds in vary- 
ing the abysmal temperatures.^ Examining the three lochs of the 
Caledonian Canal, he found that the bottom temperatures varied from 
year to year, but rose or fell simultaneously in all three lochs. The 
bottom temperatures in Loch Ness in August and September in eight 
different seasons are given in the following table : — 
Year. 
Mean of Observa- 
tions over 600 
feet. 
Mean Air 
Temperature of 
Previous Winter, 
November to 
April, 
1877 
42° -6 Fahr. 
38° -5 Fahr. 
1878 
42°-4 
40° -7 
1879 
41°-2 
34°-0 
1880 
42" -5 
39°-4 
1887 
42'-4 
39°-5 
1892 
42°-9 
38° -2 
1903 
42° -4 
4r-2 
1904 
42°-3 
39°-4 
1 Scott. Geogr. Mag., vol. xiii. p. 1, 1897. 
