TEMPERATURE OF SCOTTISH LAKES 
105 
line. Isothermals for temperatures above this are represented by 
the hnes r/z^, . . ., and for the temperatures below this by the 
lines 71-^, n.j^^ . . . 
By far the greater number of Scottish lakes belong to the tem- 
["learinc 
I 
Coolim 
3 
Heating 
Cooling 
Spring 
Sumr 
ner 
Aurumn 
Win 
Ter 
Spring 
Summer 
Aufumn 
Winrer 
r- 
Fig. 37. — Temperate Lakes. 
perate class. In summer and autumn the temperature is all above 
39° Fahr., the warmest layers of water are at the surface, and the 
temperature of the water decreases the deeper down it is situated. 
In winter and spring the water has all become cooled down below the 
Heafin^ CooWng Heating Cooling 
Spring 
ji. ■ . 
Summer 
Autumn 
Winter 
Spring 
Summer 
Aurumn 
Winter 
Fig. 38.— Tropical Lakes. 
maximum density point, and the condition of the lake is similar to 
what is found in polar lakes all the year round — the coldest water 
being at the surface. 
The larger and more important of Scottish lakes belong to the 
tropical class. Owing to their depth the temperature of their waters 
never falls below the maximum density point. At the bottom the 
