SEICHES AND OTHER OSCILLATIONS 
57 
In Table VI. are entered side by side the values of the various 
periods deduced from the whole series of observations, the values 
(up to Tg) deduced from the Hydrodynamical Theory, and the values 
deduced from the formula of Du Boys. It will be remembered that 
this last formula agrees better and better with the Hydrodynamical 
Theory as the nodality rises, and finally gives the same result. 
VI. Comparison of Calculation with Observation 
1\ by 
by 
V 
H.T.S. 
Du Boys. 
observed. 
1 
14-50 
17-81 
14-52 
2 
8-14 
8-91 
8-09 
3 
5-74 
5-94 
6-01 
4 
4-28 
4-45 
3-99 
5 
3-62 
3-56 
3-48-3-60 
6 
2-93 
2-97 
2-88 
7 
2-55 
8 
2-23 
9 
1-98 
10 
1-78 
1-70 ? 
11 
1-62 
12 
1-48 
1-54 ? 
13 
1-37 
1 -36 1 
14 
1-27 
1-31 1 
15 
1-19 
1 -15? 
16 
1-11 
1 -09 1 
17 
ro5 
The identification of the quadrinodal and quinquinodal periods 
respectively rests merely on the comparatively close agreement of 
certain observed numbers with each other and with the quadrinodal 
and quinquinodal periods deduced from the Hydrodynamical Theory 
and from Du Boys' formula. No phase observations were available 
to assist the identification. 
There is still greater uncertainty regarding the higher periods, 
most of which rest only on a single series of oscillations. Possibly 
T = 2*88 is the sextinodal period. It must, however, be borne in 
mind that the smaller the period, the greater is the danger of con- 
fusion with progressive wave disturbances, with possible transversal 
seiches, or even with secondary local oscillations due to indentures in 
the shore of the lake. 
During the observations the mean level of Loch Earn varied 
through a range of nearly 20 inches (over 50 centimetres), but a 
careful examination of the tables of values of the periods under 
different circumstances does not appear to show any correlation 
between the depth of the lake and the various periods. It follows 
that in the case of Loch Earn, within the range of the observations, 
the periods are independent of the depth. 
