ON THE TEMPERATURE OF THE FRESH-WATER LOCHS OF SCOTLAND. 409 



other observers ; and in view of the results which have been obtained by the Lake 

 Survey, much of the work which has been done in observing lake temperatures will, 

 I believe, prove to be of much less value than was hoped. 



I had thought at first to discover some definite relation between the measurements 

 of a loch and the quantity of heat stored up in it. Doubtless such a relation does exist 

 of the same nature as is suggested by Sir John Murray and Mr Pullar.* Take, for 

 example, Loch Leven and the Loch of Forfar,+ which in the month of June had a some- 

 what similar mean temperature, viz., 54*0° F. Data for these lochs are given in the 

 following table : — 



Loch. 



Volume in 



Million 

 Cubic Feet. 



Area in 

 Square Miles. 



Height above 

 Sea-level 

 in Feet. 



Volume 

 Area. 



Leven 

 Forfar . 



2195 

 51 



5-30 

 •16 



22 

 166 



11-2 

 11-4 



From these figures it seems that some relation might be discoverable between the 

 temperature of the loch and the ratio of volume to area, but it is in general so obscured 

 by varying factors that its disentanglement would entail an amount of labour which at 

 present I consider disproportionate to the value of the results obtainable. 



What I wish to do in the present paper is to give what I consider to be the history 

 of the manner in which a loch gains and loses heat throughout the year ; and though 

 my deductions are based almost entirely on observations made in Loch Ness, yet I 

 think that most of what there is to say of the temperature of Loch Ness will be found 

 to be applicable to other lochs. 



This paper is based on observations made by members of the Lake Survey ,| with 

 which for a time I had the good fortune to be associated. The material which has 

 been collected is of a unique kind. In many lochs there have been observations 

 lasting over a greater length of time, but in no case that has come to my knowledge 

 has there been so continuous a series of observations. The regular temperature 

 observations were begun by myself, in July 1903, by the establishment of a Lake 

 Survey station at Fort Augustus. At first the observations were made by means 

 of the deep-sea reversing thermometers, which are now so well known as to need 

 no description here. The Pullar and Lucas sounding machines were both used in 

 connection with these thermometers. Regular routine observations were soon begun 

 at Fort Augustus, and a number of cruises were made along the loch in the steam 



* Geographical Journal, March 1901. t Geographical Journal, January 1904. 



J The observations were carried out by Sir John Murray, Dr T. N. Johnston, Mr R. C. Marshall, Mr 

 James Murray, Mr E. R. Watson, Mr E. M. Weddbrburn, and Mr F. G. Pearcey, under the direction of Sir 

 John Murray, K.C.B., and Mr Laurence Pullar. Valuable observations were also made by the Lake Survey 

 boatmen, Philip Campbell, Fraser, Grant, and M'Donald. 



