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XVI. — The Temperature of the Fresh- water Lochs of Scotland, with special 

 reference to Loch Ness. With Appendix containing Observations made in Loch 

 Ness by Members of the Scottish Lake Survey. By E. M. Wedderburn, M.A. 

 Communicated by Sir John Murray, K.C.B. 



(Read May 28, 1906. MS. received October 24, 1906. Issued separately February 22, 1907.) 



I. Introductory. 



My object in this paper is not, as the title might suggest, to give a comparative 

 study of the fresh-water lochs of Scotland from the point of view of temperature. I 

 had hoped at one time that this would be possible, and I may again return to this part 

 of the subject of lake temperatures ; but the more I have considered the question the 

 more am I convinced that such a comparative study from the observations at my 

 disposal would be based on assumptions too fundamental and too uncertain to make 

 the conclusions reached of any great value. Consider the factors which go to produce 

 variations of temperature as they are given by Professor Forel.* Briefly, these are the 

 indirect action of the sun in heating up the atmosphere and the surroundings of the 

 loch, radiation from the loch, the effect of warm or cold water brought into the loch 

 by rivers and by rain. These are only a few of the more important factors which are 

 mentioned by Forel, but I think that anyone considering these factors will perceive 

 how slender the ground for any general conclusions must be. There is comparatively 

 little object in comparing lochs which are at any great distance from one another, 

 for the heating of a loch depends very largely on local conditions. One may be 

 sheltered from all storms by surrounding hills, while another may be in a wind-swept 

 region. One may be so overshadowed that very little direct sunlight falls on its 

 waters, while another loch close by may get all the sunshine which it is possible to 

 get. One may be fed by a large stream and have a considerable outflow, while another 

 may be comparatively stagnant. One may be at a considerable altitude, while another 

 may be in a warm valley. There is also, I think, little to be gained from a simple 

 comparison of lochs close to one another, and which may appear at the first glance to 

 be under similar conditions. For example, take some of the lochs in the Tay basin. 

 In the hope of obtaining some satisfactory data I turned to Lochs Craiglush, Lowes, 

 Butterstone, Clunie, etc.t These are at least sufficiently close to one another. They 

 were surveyed in the month of June by members of the Lake Survey within a few days 

 of one another, and temperature observations were also made in them. I then roughly 



* Le Le'man, vol. ii. p. 289. 



t See Geographical Journal, January 1904, for the Lake Survey report upon these lochs. 



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