THE FRESH-WATER LOCHS OF SCOTLAND. 



29 



Loch Chon and Lochan Dubh. These lochs were sounded on the 15th 

 May, 1900, when the surface temperature in Loch Chon varied between 

 51-8 and 54-5 ; below the surface the temperature decreased gradually 

 down to 48-5 at 60 feet, so that the range observed throughout the 

 whole body of water was only about 6. In Lochan Dubh the surface 

 temperature was slightly higher than in Loch Chon (54-7), while the 

 temperature of the deeper water was observed to be about 1 lower 

 (47 0> 6), so that in the small body of water contained in Lochan Dubh 

 the range was greater than in the larger Loch Chon, viz., 7. 



Loch Ard. Loch Ard was visited on the 5th and 6th August, 1899, 

 and again on the 16th May, 1900. The highest surface temperature 

 (64- 6) was observed in the southern prolongation of the loch in August, 

 the maximum temperature observed at the same time in the body of the 

 loch proper being 63. It will be seen that the whole body of water 

 was warmer in August, and that a drop of 10 was recorded between the 

 depths of 30 and 50 feet, the extreme range of temperature from surface 

 to bottom being 17. No steep gradient was observed in May, the 

 temperature decreasing gradually from top to bottom, the extreme 

 range observed in May being 8-7. 



Lake of Menteith. The Lake of Menteith was visited on the 7th 

 August, 1899, and the 14th May, 1900. No serials were taken in 

 August, when the surface temperature varied only from 62'2 to 63'2. 

 In May the surface temperature varied from 51*1 to 52'2, and the 

 temperature decreased gradually from surface to bottom, the range 

 observed in May throughout the whole body of water being only 2 



