130 THE FRESH-WATER LOCHS OF SCOTLAND 
the effect of producing periodic currents at the surface, and if the natural 
period of the seiche were sufficiently near the period of the wind, this 
would be a very effective cause. ^ Taking the depth of the discon- 
Fig. 51. 
tinuity as 24 feet, the length of the lake as 36,000 feet, the mean 
temperature of the water above and below the discontinuity as 67° 
1 The effect is greatest when the period of the lake is less than the forcing 
period. See Chrystal on the Seiches of Loch Earn, Trans. Roy. Soc. Edin., vol. xlvi. 
p. 514, 1908. 
