of Edinburgh, Session 1885 - 86 . 
427 
The bottom temperature has been determined in the deepest part 
of Loch Lomond by several observers in different years, and the 
results show that it varies from year to year. James Jardine 
found it to be 41 °*1 F. on the 8th September 1812. Sir Robert 
Christison found it 42 o, 0 F. in 1871. I found it to be 40 o, 2 in 
April 1872, and 41 0, 4 F. on 23rd September 1876. About these 
figures there is always some uncertainty, from the want of com- 
parison between the thermometers. The best evidence of the varia- 
tion of the temperature of the deep water of our lakes, from year 
to year, is furnished by my observations in Lochs Lochy (80 fathoms) 
and Ness (120 fathoms) in five consecutive years in the second 
week of August. These were all made with the same thermometers, 
and are to be relied on to one-tenth of a degree. They are — 
Years, .... 
1877. 
; 1878. 
1879. 
1880. 
1881. ] 
Loch Lochy, 
Loch Ness, 
Mean winter temp, of air ) 
at Corran, . . } 
44° -0 
42° -4 
42° -3 
43°-7 
42° -3 
42° -7 
42° -0 
41° -2 
38° -9 
43° -8 
42° *4 
42°*0 
42° -25 
41°-45 
38° -6 
The mean winter temperature of the air is the mean temperature 
of the months of October to March (inclusive) preceding the dates 
of observation in the lakes. The place of observation is Corran 
lighthouse, on Loch Linnhe. It is too remote from the lochs 
themselves to give more than an indication of the climate at the 
surface of the lakes. Still the bottom temperature of Loch Ness 
does follow very closely the mean winter temperature at Corran. 
In the two severe winters, 1878-79 and 1880-81, the mean 
winter temperatures fell below 39°, and as might have been 
expected the temperature of the deep water of the lake was slow 
to follow it, owing to the change in the properties of water at 
this temperature. Hence the higher the mean temperature of the 
cold months of the year is, the more closely is it reproduced in the 
deep water of the lake. Forty years ago Amie showed that the 
temperature which he observed in the abyssmal regions of the 
Western Mediterranean agreed sensibly with the mean winter tem- 
perature of the air at its surface. The later view, which ascribed 
the temperature of the deep water in the Mediteranean to the 
Atlantic water flowing over the ridge at Tarifa, which has the same 
temperature as the Mediterranean water within the ridge, left out 
