368 Alf Trolle. 



the time chosen was about the change of moon, when the changes 

 due to the tide might be considered to be maximum. 



In addition, observations were made a lew km. further north 

 in the mouth of Øresund through two changes of the current (series 

 LXVI I A and B) and also somewhat further up in Øresund during 

 the period about high water (series LXIX) (the results are noted down 

 on Pi. XIX). 



All the observations were made through holes in the ice and it 

 was possible on this steady surface to obtain great accuracy. 



Results of the observatioDs. 



It will be seen from PI. XVIII and XIX, that there was a close 

 connection between the differences just mentioned in temperature 

 and salinity and the course of the tidal wave. These differences may 

 be imagined to arise through the horizontal tidal currents in the sea 

 becoming partly transformed to vertical currents, when the tidal 

 wave entered the mouth of Øresund and passed over the ascending 

 sea-bottom (called the barrier in the following). 



The lowermost water-layers ran in parallel with the bottom, thus 

 rising upwards so as to become partly mixed with the overlying water- 

 layers, which flowed in horizontally. The amplitude in salinity varied 

 between 0.95 p. m. and 0.36 p. m. and the amplitude in temperature 

 between 0.16° С and 0.32° С The average of the amplitude was 

 0.63 p.m. and 0.23° С 



The curves (PI. XVIII and XIX compared with the observations 

 in Tab. 12) show the following features. 



The temperature and salinity curves follow very closely together 

 in the series LXIV A, B, C, D (PI. XVIII), rising water giving increas- 

 ing temperature and salinity, whilst falling water gave the opposite 

 result. The times for the highest and lowest values, however, did not 

 fall exactly at the times for high and low water. At a depth of 100 m. 

 the water sometimes flowed in after high water and out after low 

 water. 



A characteristic of the two curves about high water is the sudden 

 rise of temperature and salinity in its neighbourhood. The current 

 measurements at the surface showed, that there was still water there, 

 thus at the same time that the water at 100 m. was running in and 

 pressing upwards in a wave. Similar waves were found in series 

 LXXVII В (PI. XIX), which was taken further up in Øresund at the 

 period about high water. 



At the latter station measurements were made through two cur- 

 rent changes and the samples were taken from the depths 75, 100 

 and 125 m. as quickly as possible after each other, in order to follow 

 the variation in these depths as nearly simultaneously as possible. 



