605 
1908-9.] Observations on Deep Water Oscillations. 
Skagerak this correction is about 25 per cent, of the length,* making the 
effective length of the basin 250 km. 
In calculating the period of a temperature seiche in the Skagerak by the 
above formula, I assumed as the depth of the upper layer 20 metres and as 
its density h023. For the depth of the lower layer, I took first a depth of 
100 metres and then a depth of 200 metres. The mean depth of the basin, 
calculated by taking the square of the mean of the square roots of the 
depths marked on the chart, was about 180 metres, which gives for the 
depth of the lower layer 160 metres. It is therefore thought that the true 
period for the basin should lie between the two calculated periods. These 
were respectively 14*2 days and 13‘9 days. 
This period is in very close agreement with the period observed by Dr 
Pettersson, and to my mind there is little doubt that the oscillations are not 
tidal, but are analogous to the oscillations observed in Loch Ness and Loch 
Garry, and also in the AVolfgangsee by Dr Exner. 
Dr Pettersson also gives a few observations made at Revsnoes, in the 
Great Belt, in July 1908, which indicate an oscillation of the deeper water 
with a period of about a day. They are too few to state the period of the 
oscillation with any certainty, but a calculation similar to the above shows 
that in a basin about 25 km. long there might be an oscillation with a 24- 
hour period. The basin of the Great Belt is very irregular, and it is difficult 
to know what may be the length of the basin in which an oscillation would 
take place. It seems likely, however, that the July observations also record 
the presence of an internal or temperature seiche. On several occasions the 
observations made by Sir John Murray in the sea-lochs of the West of 
Scotland showed oscillations in the bottom dense layer of water; and 
although the observations were not continued for a sufficient length of time 
to show whether the oscillations were periodic or aperiodic, it is quite likely 
that they, too, were due to an internal seiche.f 
Pettersson ’s observations were discussed at a meeting of the “ Challenger” 
Society held on 30th June 1909, and those present were practically unanimous 
in considering the tidal effect as a minor element. Dr Everdingen, however, 
pointed out that if there was a great interchange of water with the diurnal 
tides, similar curves would result from the fact that all the observations 
were made at the same hour each day, and thus at a later phase of the tide 
which would recur in about fourteen days. It is most unlikely, however, 
that the daily tides could produce anything like a range of 100 metres in the 
level of the lower layer of water ; and the feeling of the meeting was that 
* Op. cit p. 60. 
t E.g. see observations in Locli Etive in 1888, Proc. Roy. Soc. Eclin ., vol. xviii. p. 158. 
