296 Scientific Proceedings, Royal Dublin Society. 
the fact that the stake was covered, remarking that the river 
appeared to be rising very rapidly ; not long after about 3 inches 
of the stake was again visible, and later on I again saw it covered. 
I had left home the night before in pouring rain, with a low and 
falling barometer ; but had no instrument of the kind with me. 
In a river, controlled as the Shannon is, by gates or sluices, 
it may be possible that the rise and fall was due to their influence ; 
but it is to be doubted if two successive rises, such as I observed, 
could be caused by them. At that time I was leaving for another 
part of the river, otherwise might have made more observations ; 
but it now appears to me to be a matter for consideration as to 
what effect a seiche occurring, say, on Lough Ree, above where I 
observed this rise and fall, would have on the river, 7. e. would each 
rise on the lough send down more water ? Again, suppose a seiche 
to occur on Lough Derg, in the other direction, what would be the 
effect, if any, on the river P 
Mention has already been made of the influence of the sur- 
roundings of a station on amplitude and duration of a seiche; if, 
however, it could be shown that the total effect could be observed 
in a river, flowing in or out of the lake, the element of surround- 
ings might be eliminated, as the river should give the mean of 
both amplitude and duration of the seiche for the whole lake. 
While the cause of seiches remains practically unknown, except 
that they appear to be usually accompanied by low barometric 
readings, there is much room for various conjectures, but I venture 
to hope that a more general knowledge of their existence may 
induce many, having opportunities, to keep a watchful eye for 
their occurrence. 
To give satisfactory results, synchronous observations are 
indispensable, with characteristics of the land surrounding the 
stations, and, in addition to amplitude and duration of the seiche, 
the barometer should be carefully noted ; also wind ; and if deflected 
by land, as in the case of the observation spot on Lake Derra- 
varagh. Soundings of the lake should be obtained ; perhaps, tem- 
perature of the water; also if a rise of alge to the surface 
accompanies a seiche. It would also be an interesting matter to 
know whether the rise and fall is simultaneous on the whole lake, 
or if the water is rising at one station and falling at another at the 
same time. 
