294 Scientific Proceedings, Royal Dublin Society. 
simultaneous observations could never be satisfactorily carried out, 
unless, perhaps, the dwellings were connected by telephone or 
telegraph, as an observer at a station on a part of the lake, sub- 
ject to large amplitudes, would observe a seiche that might be 
totally missed at another station where the amplitude was slight 
Self-registering gauges might be used, but a number would be 
required for simultaneous observations on a lake; the clockwork 
movement would need attention, and specially fitted protection 
from the weather, this all becoming a costly experiment. 
At Lake Derravaragh, at first, the theory that seiches might be 
due to seismal influence, appeared to be not altogether devoid of 
foundation. The abrupt manner in which the hills rise from the 
southern part of the lake seemed to point to a great depth of 
water; and local rumour currently reported that at the foot of 
Knock Hyon the lake was 500 feet in depth, or as deep as that 
hill is high above it. From the soundings taken it will be seen 
that the deepest water 89 feet, at low water of summer, is actually 
at the foot of Knock Hyon ; but this depth is really very little in 
excess of the depths generally surrounding it, and the bottom is 
singularly flat, and consists of, or is thickly covered by tenacious 
mud. 
I believe that, in the cases of some other lakes where seiches 
have been found to occur, attempts have been made to connect a 
periodical rise of an alge to the surface, with the changes of level. 
From my experience, it appears that Lake Derravaragh “ purges,” 
as it is locally termed, at all seasons of the year, 7. e. large quan- 
tities of algze rise to the surface, rendering the water turbid to the 
depth of a foot or more, and should a strong breeze be blowing at 
the time, large collections of the bright green sub-aquatic plant 
may be found in all the indentations of the lee shore. Although 
I have noted it as being on the surface prior to the occurrence of 
a seiche, it was so frequently to be seen, that it is impossible to 
form any connection between them. 
On examination! this alga was found to be Celospherium 
Riitsingianum (Nag) a plant which had been found in some parts 
of Ireland by Dr. John Barker, and shown by him at the Dublin 
Microscopical Club on 19th November, 1868. It differs from the 
1 Professor Fred. O. Bower, pD.sc., F.u.s., Glasgow University, kindly examined 
and identified this plant. 
