1903-4.] Mr E. Maclagan-Wedderburn on Seiches in Loch Ness. 25 
Seiches observed in Loch Ness. By Mr E. Maclagan- 
Wedderburn. Communicated by Professor Chrystal. 
(Read November 16, 1903. MS. received December 22, 1903.) 
{Abstract.) 
The first observations on seiches in Scotland were made last 
summer hy members of the Lake Survey, the differences in level 
having been measured by a foot-rule. A Sarasin limnograph was 
procured by the Survey and was set up at Port Augustus on Loch 
Ness in June of this year, and has been recording since then, with 
only a few stoppages. The biggest seiche so far recorded had an 
amplitude of about 9 cm. The boat-house of St Benedict’s Abbey, 
kindly put at Sir John Murray’s disposal by the Lord Abbot, gave 
shelter to the instrument both from wind and waves. 
Three types of seiches are common on Loch Ness, with periods 
of approximately 31 ‘5, 15 ’3, and 8 '8 minutes. The first of these 
is probably the uninodal seiche. It seldom occurs pure, or of any 
considerable magnitude. This may be due to the influence of Loch 
Dochfour, which is a continuation of Loch Ness at the north-east 
end. The two lochs are connected by a narrow channel about 20 ft. 
deep, through which a strong current sometimes flows, and for this 
reason, in calculating the theoretical period of the seiche, it was 
thought proper to omit Loch Dochfour. 
The period was calculated in two ways. First, by the formula 
t = 2jdl Jb/ag, where b is the breadth and a the area of a cross 
section at any particular point. This is the formula obtained by 
assuming the hypothesis of parallel sections. The value obtained 
was 42 minutes, which is considerably in the excess of the observed 
value. The period was then calculated by the formula t = 2 f dl/sjgh, 
and the value obtained for t was 30’9 minutes, which agrees very 
closely with the observed value. This method assumes that the 
period of the seiche would be the same if the shores of the loch 
rose perpendicularly instead of obliquely. 
