of Edinburgh, Session 1885 - 86 . 
421 
cated for the different pairs of dates. For convenience’ sake, heat 
units are expressed in fathom-degrees * 
From the table we see that between the 5th and 22nd September 
the water as a whole has lost as much heat as it has gained, so that 
all the heat that the layer above the intersection at 13 '5 fathoms 
has lost appears in the deeper water below the intersection. On an 
average over the whole period, no heat has been dissipated to the 
atmosphere. This, of course, is only true on an average ; for dur- 
ing the first portion of the period the water has been receiving- 
heat, and during the second portion it has been dissipating it at the 
surface. During this interval the heat passed downwards to the 
deeper layers has been at the rate of 1*94 fathom-degrees per day. 
Between the 22nd September and 15th October the amount of 
heat transmitted downwards has been 14 per cent, of the total 
loss above the intersection. The heat dissipated per day to the 
atmosphere is 2*61 units, and that passed downwards 061 unit. 
The curve of 14th November does not cut that of 15th October, 
and the loss of heat is at the rate of 3 - 2 units per day, all of 
which has gone out into the atmosphere. On the 23rd November 
1876 I found the water of the Luss basin to have a uniform 
temperature 47 0, 8 from surface to bottom. In the year 1876, there- 
fore, the water had a temperature 1°*5 higher on the 23rd Novem- 
ber than it has in 1885 on 14th November, or nine days earlier. 
For the same date the 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 no very hard or long-continued frost to freeze the 
great shallow Balloch basin of the loch. In fact, it will be found 
that in years 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 
11 fathoms. The temperature of the whole of the water was 
* The fathom-degree is one fathom heated 1° F. If the fathom has a 
sectional area such that the volume of water weighs one pound, then the 
fathom-degree is the same as the ordinary heat unit. 
