414 



MR E. M. WEDDERBURN 



shore to be influenced in very much the same manner as water near the ends of 

 the loch. No doubt the fact that there is a prevalent wind will make the typical 

 curves for one end of the loch differ from those of the other end, but such a difference 

 must be one of degree and not of kind. Fig. 1 shows the curves obtained by taking 

 monthly means over the whole period of the observations. Fig. 2 shows on an 

 arbitrary scale the quantity of heat in the loch throughout the year — this curve 

 being obtained by assuming the curves in fig. 1 to be typical for the whole loch. 



Fig. 3 shows the rate at which the curve in fig. 2 changes, and so represents the rate 

 of change of temperature. 



It thus appears that in September there is the greatest quantity of heat in the 

 loch. Thereafter the loch cools rapidly until March or April, when the water begins 

 to heat up again. It is perhaps worth while to notice that the mean air temperature 

 at Fort Augustus in March for these two years is 39 , 9° F. and in April 43*4° F., and 

 as the lowest temperature the loch reaches is intermediate to these, it is quite to be 

 expected that the loch would first show an increase of temperature in March or 

 April. And in other lochs the increase of temperature will be governed in the 

 same way. When the average temperature of the air begins to be above the surface 

 temperature of the loch, then the loch will begin to gain in heat. 



