ON THE TEMPERATURE OF THE FRESH-WATER LOCHS OF SCOTLAND. 415 



The form of the typical curves is also instructive. Prom May till August we 

 have an increase of temperature throughout the water at different depths, propor- 

 tionate to the depth. This is true of the water above 200 feet. Below that depth 

 the heating takes place more slowly, but even in the deepest water there is a range 



Surface. 



50 feet. 



100 feet. 



1 50 feet. 



200 feet. 



tilltUMlU 



Fig. 4. 



of temperature of about two degrees. The lowest recorded temperatures at the bottom 

 of the loch are in April, and the highest in the middle of November. The mean air 

 temperature of August for the two years is 54*8°, and of September 53"0°. The 

 highest temperature of the surface layers is about 55°, though, of course, there are 

 often higher temperatures recorded. Fifty-five degrees may be taken as the mean 

 TRANS. ROY. SOC. EDIN., VOL. XLV. PART II. (NO. 16). 59 



