424 



MR E. M. WEDDERBURN 



the question by the observations which were taken in September 1904, the results of 

 which are represented in fig. 7, which has already been explained. The opposition 

 between the curves for Fort Augustus and Dores is as good as could have been hoped 

 for. Most unfortunately, from this point of view the temperature seiche which was 

 in progress when the observations were commenced was disturbed by the wind 

 changing from N.E. to S.W. about the 16th, and so all the warm water was carried 

 towards Dores. The effect of a change of wind (it may be of degree) is to disturb 

 any existing seiche. This is due, no doubt, to the damping effect of the currents set 

 up by the wind, and also to the change in the distribution of the water, which 

 means a difference in the period of the seiche and also a displacement of the node, 



Fig. 10.* 



This explains the sudden and continuous rise in temperature shown in the Dores 

 curve. The Inverfarigaig curve shows much less disturbance than either of the other 

 two curves, and this points to the presence of a node somewhere in its vicinity. Most 

 of the disturbance which is shown on the Inverfarigaig curve would seem to be due 

 to a binodal seiche of approximately half the period of the fundamental seiche, which, 

 from these curves, appears to be about two days. A rough calculation of the period 

 agrees very closely with this observed value. The mean depth of the loch may be 

 taken as 450 feet. Fig. 10 shows two temperature-depth curves for this time of year, 

 from which it appears that the depth of the surface layer may be taken as 150 feet. 

 This leaves for the mean depth of the cold layer say 300 feet. The mean temperatures 

 of the layers for the purpose of this calculation may be taken as 54° and 43° respec- 

 tively. Employing the formula 



f _ 21 



p - + p -, 

 h h 



I, Invermorriston, noon, 13th September 1904 ; II, Inverfarigaig, noon, 17th September 1904. 



