102 
Proceedings of the Poyal Society of Edinburgh. [Sess. 
Comparing this table with the temperatures given in Table I., which 
are, as already explained, a rough measure of the heat supplied to the 
lake, it is seen that when the river temperature is below the surface 
temperature the lake is losing heat, and when it is above the lake is gain- 
ing in heat. Thus in the middle of February there was a very mild spell 
of weather during which there was an accession of heat, followed by very 
cold weather during which there was a considerable loss of heat, and the 
second week of March is the time at which the lake is at its coldest. There- 
after there is a steady accession of heat until the middle of June, the most 
rapid gain being during the warm and sunny weather which occurred about 
the end of May. About the middle of June there was actually a loss of 
heat. The weather during a large part of June was sunless, and during 
the week ending 22nd June the mean maximum air temperature was under 
50° F. In the end of June and beginning of July there was again a spell of 
warm weather followed by an accession of heat, but during the sun] ess 
weather of the third week of July there was again a loss of heat. As the 
observations were discontinued shortly thereafter, I cannot say whether 
this loss was arrested, or whether the lake continued to lose heat during 
the autumn. 
During the period of observation the difference between the greatest 
and least quantity of heat in the lake is about 9 X 10 14 gram calories, which 
may be considered as the quantity of heat stored up in the lake during 
spring and summer. For Loch Ness I calculated that the quantity of heat 
stored up was 1*9 X 10 16 gram calories, which is more than twenty times as 
much as in the case of Loch Garry, while the area of Loch Ness (through 
which the heat enters the lake) is only twelve times that of Loch Garry. 
According to Knott the solar energy supplied is equivalent to 60 - 73x 10 14 
gram calories. 
The disparity between the ratios of surface area to quantity of heat in 
Loch Ness and in Loch Garry may appear at first surprising, but when the 
quantity of water passing through Loch Garry, and the fact that it is the 
warmest surface water which flows out of the loch, is considered, it is 
apparent that more heat is lost by this means in the case of Loch Garry 
than in the case of Loch Ness, where the outflow is comparatively very 
small. Another reason for the smallness of the ratio in the case of Loch 
Garry is that owing to the less bulk of water the surface water rises in 
temperature much more rapidly than in Loch Ness, and accordingly the 
date at which the lake ceases to gain in temperature by conduction is much 
earlier. Moreover, though no sunshine observations are available, I think 
it is safe to state that the average amount of sunshine over Loch Garry is 
