president’s address. 
167 
iodo-bromide of silver. For the Lake of Geneva the greatest 
depth at which any darkening of the plate took place was 
between 200 and 240 m. 
The movements of the water in the large lake basins has 
been minutely studied, especially in the Lake of Geneva, 
the Balaton-see, and the Hallstiitter-see ; and a great deal 
has been written upon a curious phenomenon, which, though 
the effects have long been familiar to the people of Geneva, 
has only lately been recognised as a common one on lakes 
of large volume ; I mean the currents or waves, to which the 
name “ seiche ” has been applied. This is caused by changes 
in the barometric pressure, which produce, as it were, a rocking 
of the contents of the lake basin ; this forms a wave or tide, 
which is indicated by a rising or falling curve on the recording 
chart of the limnograph or tide gauge. This wave may be 
simple or uninodal, or there may be a movement about two 
axes, which produces a binodal seiche, or there may be 
a more complicated motion, which Forel has called a plurinodal 
seiche, and a fourth kind, formed by the clashing of a uninodal 
and a binodal seiche, to which he has given the name dicrotic. 
I show upon the table charts and diagrams to explain 
these several forms of seiche, taken on the Lake of Geneva 
and Balaton-see. 
A curious seiche is that shown for Balaton-see, which gives 
a similar curve to that for a marine tide, with two rises and 
two falls in the twenty-four hours. 
Seiches have been detected in the Scotch Lochs and on 
Lake George in New South Wales as well as in various lakes 
on the Continent ; but they have been studied most fully in 
the two lakes named above. 
Besides movements due to this cause, there are waves 
caused by earth tremors and by wind, and these waves 
often obscure the movements due to seiches. A curious form 
of disturbance, which troubled Forel, was caused by steamers, 
