338 On the Distribution of Temperature in 



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 42-0 F. in 1871. I found it to 

 be 40-2 in April 1872, and 41*4 F. on 23rd September 1876. 

 About these figures there is always some uncertainty, from the 

 want of comparison between the thermometers. The best 

 evidence of the variation 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 



The mean winter temperature of the air is the mean tem- 

 perature of the months of October to March (inclusive) pre- 

 ceding 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 indica- 

 tion 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 temperature 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 Aime showed that the temperature 

 which he observed in the abyssmal regions of the Western 



