332 On the Distribution of Temperature in 



water is this year at least 2-5 colder than it was in 1876, and 

 with this rapid and severe autumnal cooling it will require 

 n-> vi-ry hard or long-continued frost to freeze the great shallow 

 Balloch basin of the loch. In fact, it will be found that in 

 - when Loch Lomond has been frozen there has always 

 been an exceptionally cold autumn. The prolonged action of 

 the low temperature of a cold autumn prepares the water for 

 any severe frost which may occur in the long nights about 

 Christmas. Under its influence the water rapidly freezes. 

 When the Balloch basin was frozen in the winter of 1878-79, 

 I took the temperature of the water beneath the ice in several 

 places, the deepest water being n fathoms. The temperature 

 of the whole of the water was under 35 F., and varied from 

 32 in contact with the ice to 34-5 at the bottom. In the long 

 clear nights of a severe winter the temperature of the atmosphere 

 may often be 30 below that of the surface of the water, so 

 that both by radiation and convection cooling goes on with 

 great rapidity, notwithstanding the fact that water expands 

 in being cooled below 39 F. ; and it is remarked by people 

 dwelling by the side of the lake that the moment ice begins to 

 freeze it spreads with great rapidity, so that the whole basin is 

 usually frozen over in a night, and as soon as a skin of ice has 

 been formed it very rapidly becomes thick enough to bear. 



Epochs of Maximum Temperature. From the curves and 

 their intersections we see that the maximum temperature of 

 the surface water occurred before the 5th September. At 

 13-5 fathoms it occurred some time between the 5th and 

 22nd September, and as cooling goes on faster than heating, 

 the date of maximum temperature at this depth will be nearer 

 the 22nd than the 5th September, probably about the I5th. 

 Similarly at 16 fathoms it occurs between the 5th September 

 and I5th October, and probably about 3oth September. 

 At 19-5 fathoms the maximum temperature occurs about 

 6th October, and in the second week of October (in 1885) all 

 water from 20 fathoms to the bottom attained and passed its 

 maximum temperature. The maximum temperature of the 

 surface occurs about the middle of August, and that of the 

 bottom in 35 fathoms about the middle of October. 



