60 
THE FRESH-WATER LOCHS OF SCOTLAND 
termination of the Middle Trinode were rendered useless by casual 
wind-disturbances. 
Western Trinode. — No observations of sufficient accuracy were 
available. 
Effect of Meteorological CoNorrioNs upon the Denivellation 
OF Lakes 
General Character of the Seiches on Loch Earn. — Owing to 
the comparatively regular shape of its basin, and the fact that the 
depth is considerable compared with the length, the seiches on Loch 
Earn are very regular and very persistent. Also, probably because 
its longest axis is more or less parallel to the paths of the major and 
minor atmospheric disturbances,^ Loch Earn is very rarely free from 
seiches. During 1070 hours, from 10th August to 28th September, 
the waggon recorder at Picnic Point was almost constantly in action ; 
yet only 2| hours of calm ^ were recorded. During 1350 hours, from 
12th October to 7th December, while the waggon recorder was in 
action at Lochearnhead, there were in all about 90 hours of calm. Of 
these, 81 hours were made up by continuous stretches of 21'% 2T\ and 
23^ on 4th, 16th, and 20th November. 
The greatest ranges observed in August and September were 
79 mm., 66 mm., 73 mm., 55 mm., 55 mm., 63 mm., on 19th and 
21st August and 3rd, 7th, 8th, and 9th September respectively. Only 
one very exceptional range was observed between 12th October and 
7th December, viz. 55 mm. on 7th December. 
The range of the seiche at St Fillans is usually over 10 mm. A 
rough estimate showed that during the 1070 hours of observation at 
Picnic Point the range of the seiche was over 30 mm. during 214 
hours ; and during the 1350 hours at Lochearnhead it was over 30 
mm. during 57 hours only. It follows that, whether we test by hours 
of calm, by hours of excess over 30 mm., or by occurrence of 
exceptional ranges, the period from 12th October to 7th December 
showed much less seiche activity than the period from 10th August 
to 28th September. 
In more or less settled weather, by far the commonest seiche 
confio-uration on Loch Earn is a uninodal and binodal dicrote.^ 
This varies between the two extremes where the binodal on the one 
1 See my paper, " On the Theory of the Leaking Microbarograph, etc.," Proc. 
R.S.E., voL xxxviii. p. 454, 1908. 
2 I.e. whole range of seiche less than 2 mm. 
3 For brevity, in what follows such a seiche will be denoted by " UB-dicrote." 
Similarly, " UBT-tricrote " would mean a tricrote seiche with uninodal, binodal, 
and trinodal components, and occasionally the amplitudes (half ranges) of these 
components will be denoted by U, B, T, respectively. 
