146 Proceedings of Royal Society of Edinburgh. [sess. 
While the seiche may best be generated by motion transferred 
to the liquid in the neighbourhood of a node, the natural period 
can only be satisfactorily determined when the liquid is left to 
oscillate freely by itself. 
The principle of resonance enables us to overcome the difficulty 
involved in the ignorance of the true periods. If any motion 
except that approximating closely to a natural period of oscillation 
be imposed upon the liquid, it will not respond to any extent, and 
no seiche results. By communicating the motion by hand and 
regulating the impulses by the responsiveness of the water, the 
latter could be made to oscillate in some cases in as many as five 
or seven different periods. After the various seiches had been 
produced in this manner by repeated trials, varying the timing 
of the impulses and the position of application of these, the 
periods of the free oscillations of the water were observed and 
noted. 
The following tables show the relation between the calculated 
and the experimental results for the particular curves mentioned : — 
Tabulated Results. 
[A.ih — The experimental error-limit in the case of the periods 
tabulated, involves a correction of ± -02 seconds ; and in the 
case of the distance of the nodes from the centre, a correction 
of ± 2 cm.] 
N.B . — The references are to the Trans. Roy. Soc. Edin ., vol. 
xli., part iii. (No. 25). 
1. Seiches in a concave symmetric complete parabolic lake [§ 27], 
N.B . — All linear measurements are in centimetres; the periods 
are given in seconds. 
A r a 0_ cl A 
A 
[a =70 cm.; h =10*9 cm.] 
