422 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. 

 ByE. 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 4J 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 31-5 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 ChrystaFs 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 Dores 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. 



