ON THE TEMPERATURE OF THE FRESH-WATER LOCHS OF SCOTLAND. 427 



all through, and this may be due to a similar reason, but it is worth while to 

 notice here that many of the limnograms for Loch Ness also show curves with flat 

 tops, and the reason may perhaps more correctly be sought in the shape of the basin 

 of the loch. It is quite possible that when the lower layer of the loch acts so 

 independently the upper layer should also act independently, and from this point 

 of view I have examined limnograms for the time of year when the Sprungsohicht 

 is best marked. In some of the records there seemed to be a trace of a seiche in the 

 upper layer alone. In no case, however, was the evidence sufficiently clear to warrant 

 a definite assertion. 



VI. Floods. 



Reference has already been made to the influence of rivers on the observations made 

 at Fort Augustus, and I now wish to refer to the effect produced by heavy floods, and 

 as an example I shall take the floods which occurred in the middle of October 1903. 



i 



i?V*Octx>ber l SOS. 



Fig. 13. 



There was very heavy rain on the evening of the 1 5th, which continued till the evening 

 of the 1 6th. Both the rivers, the Oich and the Tarff, came down in flood. The first 

 effect noticeable was a great lowering of temperature at Fort Augustus, owing to the 

 water brought down by the rivers being colder than the mean temperature of the loch. 

 An effort was made to determine whether the temperature distribution at Fort Augustus 

 was typical of the whole loch, and for this purpose numerous thermometrical soundings 

 were made in the neighbourhood of Fort Augustus, with very interesting results, shown 

 in fig. 13. It appears from this diagram that the distribution at Fort Augustus is 

 very local, and that at a distance of about one mile the effect of the floods is not great. 

 One very interesting point is that the water brought down by the rivers seems to keep 



