48 
THE FRESH-WATER LOCHS OF SCOTLAND 
The determination of the nodes was subject to a large experimental 
error, but the agreement with the theory for the lower nodalities was 
also as near as could be tested. 
The tables for the complete and semi-parabolic lakes afford a 
verification of the curious theoretical result that in lakes of that form 
the seiche periods are independent of the rise and fall of the lake surface. 
Composition of Seiches, and the Analysis of a Limnogram 
BY ReSIDUATION 
If two seiches of the same period, whose amplitudes and phases 
may be different, be superposed, the result is a seiche of the same 
Fig. 16. 
period whose amplitude and phase can be calculated, and are not in 
general the same as the amplitude and phase of either of the com- 
ponent seiches. This will be understood from the seven cases given in 
fig. 16, in which the thin and dotted lines represent the component 
seiches, and the thick line the resultant compound seiche, the ordinate 
of which is the algebraic sum of the ordinates of the components. 
In the particular case. No. vi., where the amplitudes of the com- 
ponents are equal, their periods equal, and their phases differ by half a 
