118 THE FRESH-WATER LOCHS OF SCOTLAND 
Observations at Centre of Loch Garry, June 1908. 
Depth. 
6th. 
8th. 
9th. 
10th. 
11th. 
12th. 
13th. 
15th. 
16th. 
17th. 
18th. 
19th. 
20th. 
Surface 
56-8 
52-2 
53-1 
52-8 
52-8 
52-0 
51-9 
51-8 
51-4 
51-9 
52-0 
52-2 
52-0 
25 feet 
50-5 
51-5 
50-0 
52 0 
51-9 
52-0 
51-8 
51-5 
51 -2 
51-3 
51-1 
51-4 
51-5 
• 50 
48 0 
50-9 
48-9 
48-7 
49-0 
50-4 
51-0 
51-3 
51-1 
51-0 
50-5 
50-5 
50-9 
75 
47-0 
49 0 
47-0 
47-0 
46-7 
47-0 
46-8 
46-7 
47-6 
47-0 
47-6 
47-5 
47-3 
100 
46-0 
45-9 
46 4 
46-2 
46-2 
46-4 
46-3 
46-3 
46-0 
46-3 
46-2 
46-4 
46-2 
150 
45-8 
45-7 
45-9 
46-0 
46-0 
46-0 
46-0 
46-0 
46-0 
46-0 
46-0 
46-0 
46-0 
200 „ 
45-5 
45-5 
45-8 
46 0 
45-8 
45-9 
45-9 
46-0 
46-0 
46-0 
46-0 
46-0 
46-0 
The discontinuity is not always well marked. Fig. 47 shows a 
typical distribution of the isotherms in Loch Ness. It is drawn from 
the observations made on 17th September 1904. The diagram 
represents a longitudinal section of the lake, the depth scale being 
much exaggerated in comparison with the horizontal scale. On this 
diagram isothermal lines are drawn for every two degrees Fahr. 
This diagram will be referred to later in dealing with the effect of 
winds, but it is referred to here in order to show that the discontinuity 
may be very marked at one end of the lake, as shown by the bunching 
together of the isotherms, and not nearly so marked at the other end. 
On the date in question there was a fall in temperature through 50 
feet of 9° '4 at Dores (at the north-east end of the lake), while at Fort 
Augustus the greatest rate of fall was 4"'0 in 50 feet — considerably 
less than half. The temperature gradient was at times very large on 
Loch Ness, falls of 5° in 25 feet being common, and at times the fall 
was as great as 8° in 25 feet. 
With such rapid temperature gradients, it is not strange that in 
the neighbourhood of the discontinuity there are rapid changes of 
temperature. These were well shown by means of the electrical 
thermometers and recorder. Fig. 44 is a reproduction of one of the 
records obtained on 18th August 1904, with the platinum thermometer 
at a depth of 100 feet.^ Temperature is measured along the abscissa, 
and time along the ordinate. The embroideries on the curve cor- 
respond to variations in temperature up to 2" Fahr. 
It may be that more than one discontinuity is formed in a lake. 
If two discontinuities are formed, the lake is divided into three layers. 
An example of this was found in the Wolfgangsee, and will be 
referred to later. 
The depth at which the discontinuity is found varies greatly with 
different lakes. In Loch Ness it first made its appearance at a depth 
of about 100 feet; but in comparatively shallow lakes the discon- 
1 The temperature scale of the recording thermometer was not accurately 
determined, but the range of temperature shown on the diagram is about 5° Fahr. 
