52 
THE FRESH- WATER LOCHS OF SCOTLAND 
By properly adjusting the relation of the access tube to the well, 
the limnogram may, therefore, not only be stripped of its embroidery 
of short-period disturbances, but to a considerable degree the pro- 
minence of seiches of higher nodality may also be reduced, and thus 
to some extent the lake made to do its own residuation. 
Fig. 18 shows the lag and damping as seen in actual practice. 
The two limnograms AB and DE were taken with a 6-inch well 
and an access tube 6 feet long and J-inch diameter ; but the part 
CD was taken with two access tubes each 6 feet long but J-inch 
diameter. The curves A to B and C to E, save for the short break at 
D when the tubes were changed on one of the two limnograms, were 
taken simultaneously at the same spot. The lag and the damping 
may be seen on comparing CD with the corresponding part of AB, 
also the greater smoothness of CD as compared with AB and DE, 
<tl 5 10 IS ZO Zi 30 JS to IS 50 is 60 
Fig. 18. 
although the embroidery on these latter parts is very imperfectly 
rendered in these limnograms, which w ere plotted from eye observations. 
Comparison of the Hydrodynamical Theory with Oeservation 
The hydrodynamical theory of seiches is merely a development 
of the fundamental idea of Forel that a seiche is a standing oscillation 
of the lake as a whole, whose periods and nodes are dependent solely 
on the form of the lake-basin. The further this idea is carried into 
detail, the more of the varied seiche phenomena it is found to explain. 
Perhaps the best account of the present state of our knowledge of 
this matter will be found in the excellent review by Endros already 
referred to.^ 
Before proceeding to minuter details regarding Loch Earn, the 
following pair of tables compiled from various sources may help the 
reader to appreciate the variety of seiche phenomena, and to under- 
stand the relation as to seiches between home and foreign lakes : — 
^ I ought also to refer the reader to a very thorough and highly interesting 
discussion by Defant of the seiches of the Lake of Garda, Sikher. Ahad. Wiss. 
Wien, Bd. cxvii., 1908, published since the above was written. 
