276 



BATHYMETRICAL SURVEY OF 



These serials indicate a most remarkable range of temperature a 

 range amounting to 21-2 from the surface to a depth of 70 feet on 

 August 11, 1901, and 19 0t l from the surface to a depth of 60 feet on 

 August 23, 1901 ; the range observed in 1902 was much less, viz., 13'5 

 from the surface to a depth of 100 feet. Down to a depth of 25 feet the 

 readings were higher in 1901 than in 1902, but beyond that depth the 

 temperature was lower in 1901 than in 1902. The greatest fall of 

 temperature was observed between the depths of 25 and 40 feet in both 

 seasons, but the decrease of temperature within this interval of 15 feet 

 amounted in 1901 to 13-3 and 13-4, while in 1902 it amounted only to 

 8. The only observations that may be compared, as regards range 

 of temperature, with these in Loch Achilty, were taken in Loch Mon- 

 zievaird* in the Tay basin on June 8, 1903, when the range amounted 

 to 20 0< 6 from the surface to a depth of 36 feet, and when a fall of 

 temperature equal to l-5 per foot of depth was'observed between 5 and 

 15 feet. The temperature conditions observed in Loch Achilty (as well 

 as in Loch Monzievaird) may probably be ascribed to (1) the com- 

 paratively great depth, (2) the comparatively small drainage area, 

 and (3) the sheltered position, the thickly wooded shores tending to 

 temper the force of the winds blowing across the surface of the water. 

 Mention may here be made also of the large range of temperature 

 observed in the little Loch Dubhf in the nan Uamh basin on July 12, 

 1902, when the range amounted to 15| from the surface to a depth of 

 100 feet ; it is possible that under favourable weather conditions, and 

 later in the season, the range of temperature in the waters of Loch Dubh 

 may equal that observed in Loch Achilty. 



* See p. 120. 



f See p. 255. 



