SEICHES AND OTHER OSCILLATIONS OF 
LAKE-SURFACES, OBSERVED BY THE 
SCOTTISH LAKE SURVEY 
By Professor G. CHRYSTAL, M.A., Sec. R.S.E., etc. 
Historical 
Every observer of Nature is aware how inconstant a thing is the 
level of a lake at any particular point of observation. Every passing 
puff of wind, a diving duck, a rising trout, a steady breeze, a storm- 
wind, a landslip, all affect it less or more. But there is one kind of 
denivellation which is more commonly present than any other, and 
yet is so apt to escape the ordinary observer unprovided with special 
apparatus, that until about six years ago it could not truly be said to 
be known in the lakes of Scotland. On an absolutely calm day, when 
there is neither wind nor rain nor snow, and the surface of a lake is 
mirror-smooth, and to the unaided eye seems absolutely motionless, 
careful measurement, even with such a rough apparatus as a foot-rule, 
will very often — in some lakes, nearly always — show that the surface 
of the water at any point is continually rising and falling with a 
rhythmical movement. Simultaneous observations at different parts 
of the shore will show that the whole of the water of the lake 
participates in this movement. The movement may be simply 
harmonic, i.e. like the swing-swang of a clock-pendulum ; or it may 
be more complicated, and, although there may be synchronism 
between the movements in different places, these movements may not 
be everywhere alike. To take the simplest of all cases, there may be 
no vertical movement at a particular place (called the uninode), with 
vertical movements increasing in range ^ towards the end of the lake 
on one side of the uninode, and on the other side simultaneous 
vertical movements always in the opposite direction, increasing in 
range towards the other end of the lake. As will be explained 
1 By the " range " of a seiche at any point is meant the vertical distance 
between high and low water. Half this distance is called the " amplitude." 
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