No. 21. [From Proc. Roy. Soc. Edin. 1885. Vol. xm. pp. 403 408.] 



ON THE DISTRIBUTION OF TEMPERATURE 

 IN LOCH LOMOND DURING THE AUTUMN 

 OF 1885 



IN the course of the autumn of this year (1885) I have taken 

 several occasions to determine the distribution of temperature 

 in the water of Loch Lomond. The results of these observations 

 are interesting, as indicating the march of temperature in the 

 different layers at different localities in the lake, and also the 

 gain and loss of heat with the changing seasons. 



Loch Lomond is divided naturally into three basins 1 . If the 

 level of the water were reduced by about eight fathoms, it 

 would form three lakes the upper and largest extending from 

 the head of the loch to Rowardennan, the middle one from 

 Rowardennan to the chain of islands stretching from Luss to 

 Balmaha, and the third, and shallowest, from these islands to 

 Balloch. The ridges which separate these basins are covered 

 in the present state of the lake by from five to eight fathoms of 

 water. The lowest, or Balloch basin, is of great extent and 

 comparatively shallow, having a maximum depth of 13 fathoms. 

 The middle, or Luss basin, is also of considerable extent, and 

 has a maximum depth of 35 fathoms. The upper, or Tarbet 

 basin, is long and narrow, and very deep, the maximum depth 

 being 105 fathoms. At the upper end of this basin is a sub- 

 sidiary one, which I call the Ardlui basin, with a maximum 

 depth of 34 fathoms, and separated from the main basin by a 

 ridge with a probable maximum depth of 17 fathoms. 



The general direction of the lake is north and south, so that 



the prevailing westerly and south-westerly winds blow across 



it, and, as is always the case in mountainous districts, they are 



diverted into squalls, which blow sometimes up and sometimes 



1 See Chart of Loch Lomond, p. 339. 



