Mac Fartane—Seiches in Lake Derravaragh, Co. Westmeath. 291 
From the mean of a number of observations the duration of 
the seiche was 39 minutes; and it was observed that the time 
occupied by the rising was less than that of the falling in the 
proportion of about 8 toll; ze. the time of rising occupied 
about 16 minutes and falling 22 minutes; this was also noticed 
in subsequent observations. 
9th December.—Calm weather ; amplitude of seiche 4°26 inches. 
Duration of seiche (mean of fifteen observations), 37°2 minutes. 
Barometer in the afternoon 29°65 rising. 
10th December.— Barometer 29°20 amplitude of. seiche in 
the forenoon 1-5 inches, increasing to 31 inches in the afternoon. 
Duration 39 minutes. 
11th December.—Barometer 29.45 ; greatest amplitude during 
the night 3:1 inches, decreased to 1 inch in the morning. 
12th December.—Barometer 29°60 ; amplitude about 0°5 
inch. 
From the 9th to 12th December, calms and light breezes with 
fine weather generally prevailed; but from the 138th to 17th, the 
lake was rising steadily from heavy rains; and in this condition the 
character of the seiches was entirely altered, and no satisfactory 
observations could be taken. 
8rd Observation.—On the morning of January 27th, it was 
blowing in heavy squalls from the S.W., and the lake was rising 
and falling too quickly for observation ; but towards the afternoon, 
the wind having shifted to N.W., and somewhat subsided before 
dusk, the rise and fall had become steady and a few observations 
were taken :-—Amplitude 5-1 inches ; duration about forty minutes ; 
barometer 29°50 inches. 
I should feel inclined to divide the seiches occurring on Lake 
Derravaragh into two classes. 
J. Gradual rise and fall, when observations of amplitude and 
duration of seiche may be recorded. 
This class appears to occur only when the lake is otherwise at 
rest, or rather when it is not receiving any accession of water from 
rainfall, and during the year that I remained at Lake Derravaragh 
was only noticed on three occasions. 
It has been previously stated that on the 8rd and 4th October 
the weather was calm ; during the 8th December blowing a gale ; 
on the 9th of December again a calm; and on the 27th January, 
