408 



MR E. M. WEDDERBURN 



calculated the mean temperature for the lochs from these observations. The following 

 table shows the data for these lochs : — 



Loch. 



Mean Depth 

 in Feet. 



Volume in 



Million 

 Cubic Feet. 



Area in 

 Square Miles. 



Height above 

 Sea-level 

 in Feet. 



Mean Temp* 



Degrees 



Fahrenheit. 



Craigiush 

 Lowes . 

 Butterstone . 

 Clunie . 



16 

 20 

 11 



29 



49 

 194 



53 

 170 



•11 

 •34 



•17 

 •21 



328 

 328 

 314 

 156 



50° 

 53° 



58° 

 51° 



It will thus be seen that there is no obvious relation between the mean temperature 

 and the other data for a loch. I have very little doubt that in this case the most 

 important factor is that the first three of these lochs all drain into one another ; and so 

 we have the warm water of one loch draining into the next loch and there getting 

 further heated up before passing on, and so forth. Clunie is not in the same string 

 as the first three lochs, but is at a much lower level. Though it is considerably larger 

 than Loch Craigiush in every respect, yet it is actually of a higher mean temperature. 

 These lochs were chosen merely as examples to show how difficult it is, in the absence 

 of the most complete meteorological and geographical information, to arrive at any 

 exact conclusions. 



There are difficulties of even graver importance. I have so far assumed that the 

 observations from which I have arrived at the mean temperature of the lochs are 

 sufficient for this purpose, and doubtless they are in the case of small lochs such as 

 those already referred to. But this is by no means so in the case of the larger lochs. 

 Sir John Murray t and Mr Fred P. Pullar have pointed out how impossible it is to 

 deduce the temperature of the surface water from an isolated observation or from 

 observations in one part of the loch. From what follows it will appear that not only 

 is it impossible to tell anything of the surface temperatures of one part of a loch from 

 observations made in another part, but also how it is in a far greater degree impossible 

 to deduce the average temperature of a large loch from observations made in any one 

 place, or even from observations made in different parts of the loch if they are made 

 at different times. Before any satisfactory comparison of the temperature of the 

 larger lochs of Scotland is possible, a more detailed thermometrical survey will be 

 necessary. In Loch Morar, for instance, a number of observations were made at 

 intervals for the purpose of such a comparison ; but it was later realised that such 

 isolated observations as were made were futile, and the observations were discontinued. 

 The importance of the fact that observations in one part of a loch are not typical of 

 the temperature of the loch as a whole has not, I think, been sufficiently grasped by 



* Unless otherwise stated, the temperature scale is always Fahrenheit, 

 t Geograjihical Journal, April 1900. 



