SEICHES AND OTHER OSCILLATIONS 
85 
with the periods of the wind fluctuations, as indicated on the anemo- 
gram, but without success, possibly owing to the fact that the time scale 
of the anemograph was so short that it was impossible to count the 
wind fluctuations with any certainty. 
The simultaneous limnograms taken on Lochs Earn and Tay 
during October and November 1905 were examined to see whether 
there was any connection between the vibrations on the two lakes 
pointing to a common atmospheric cause. It was found that the 
average of -the maximum ranges and of the periods was much the 
same for both lakes, but there seemed to be no connection between 
the occurrence of a particular range or a particular period in the two. 
The range might be high in both lakes and the periods different; or 
the periods nearly the same and the ranges different ; or there might 
be vibrations of considerable range on one of the lakes, and none, or 
only the merest tremor, on the other. 
Several suggestions have been or may be made regarding the 
nature of these lake vibrations. 
1. They might be longitudinal seiches of very high nodality. This 
was the suggestion put forward tentatively by Forel, after trying in 
vain every other explanation that occurred to him. 
If the period of 1*47™ were due to a longitudinal seiche, the number 
of the nodes would be 12 or 13. It is easy, bv regarding Loch Earn 
as a symmetrical rectilinear lake,^ to calculate roughly the positions 
of the nodes. It would therefore be possible, by means of careful 
experiments with two or more self-registering instruments, such as 
the statolimnograph, to obtain positive or negative evidence regard- 
ing the truth of the hypothesis that the vibrations are wholly or 
partially plurinodal longitudinal seiches. 
In the present state of knowledge the balance of evidence seems to 
be against this hypothesis. A plurinodal seiche is a simultaneous 
oscillation of the whole lake. If, therefore, a vibration were a 
plurinodal seiche, it should be apparent simultaneously at both ends 
of the lake, whereas we know that it may be present at either end 
and apparently absent at the other. Also, if it be a plurinodal seiche, 
it should be present simultaneously at nearly opposite points on the 
,two sides of the lake. 
Repeated attempts were made to detect correlations of phase, by 
stationing observers on the two sides, and signalling the maxima or 
minima of the vibrations ; but it was quite impossible to establish 
either coincidence or opposition of phases. Observations were also 
made with the statolimnograph at a point opposite the limnograph 
near the eastern binode, while the latter was running at high speed 
(2'96 mm. per minute). Not only were there no apparent coincidences 
1 See H.T.S., p. 639. 
