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BATHYMETRICAL SURVEY OF 
period varied with the time of year, according to the depth of the 
discontinuity layer, and was from two to three days, which agrees 
remarkably with the periods obtained by calculation. 
Notes on the Seiches of Loch Ness. 
By E. M. Wedderburn, w.s., ll.b. 
In June 1903, observations on seiches were begun in Loch Ness by 
the erection of a Sarasin limnograph in the boat-house of St. Benedict’s 
Abbey, Fort Augustus. This instrument worked well during the period 
it was in use, and some good records of seiches were obtained. The 
largest seiche recorded by it occurred on November 21, 1903, and had 
an amplitude of about inches, but after about two days it was 
disturbed by the starting of another seiche. 
In the summer of the succeeding year a second Sarasin limnograph 
was erected at Inverfarigaig, but it did not work satisfactorily — perhaps 
owing to the exposed situation — and the records obtained were con- 
sequently not looked upon as being entirely trustworthy, although, as 
was to be expected, they pointed to a node in the neighbourhood of 
Inverfarigaig. 
Observations were also made by means of Forel’s plemyrameter, 
but owing to the exposed character of the shore all along Loch Ness, 
observation by this means was very difficult. It is unfortunate that the 
index limnograph subsequently used by Professor Chrystal had not been 
designed while work was being carried on in Loch Ness. 
The observed periods of the uninodal and binodal seiches in Loch 
Ness are approximately 3L5 and 15*3 minutes respectively. Loch Ness 
thus belongs to that class of basins in which the period of the binodal 
seiche is less than half the period of the uninodal seiche. The periods 
for Loch Ness have not been calculated according to Chrystal’s theory — 
an exceedingly laborious piece of work, which it is hoped will yet be 
undertaken — but the writer has every reason to believe that calculation 
would agree with observation in this case also ; for the basin of Loch 
Ness is convex at Foyers, where the floor of the loch rises some 200 
feet, and, moreover, the sudden shallowing which takes place in the 
loch from Lores to Bona has the effect of increasing the ratio between 
the periods of the uninodal and binodal seiches. This is seen in the 
Lake of Geneva, where there is also a shallowing at one end of the 
lake, and where the period of the uninodal seiche is more than double 
the period of the binodal seiche. 
Seiches of shorter period were also of frequent occurrence, notably 
a seiche with a period of about 8‘8 minutes, of which some remarkably 
pure records were obtained, although they were of small amplitude. 
