Hydrographical Observations from the Danmark Expedition. 367 



samples and bringing them to the ship, though the dark and the tem- 

 perature about — 30° presented considerable difficulties. 



Titration of the samples showed, however, that it was impossible 

 under such ипГал' ourable conditions to completely escape from getting 

 snow-flakes in the bottles and other causes of inaccuracy, which made 

 the value of the investigations at this season problematical. In ad- 

 dition, both of the Richter reversible thermometers were broken on 

 a journey over the screw-ice in the first winter. Taught by these 

 experiences, we did not attempt any investigations in the %vinter of 

 1907—08. 



As the station lay in a deep channel running in from the sea some 

 kilometers into Øresund (see PI. XIV), the hydrographical condi- 

 tions were very nearly the same as in the sea, as is apparent from 

 Sect. II, PI. XVI (note agreement between series LXXIII and the 

 series for the stations in the coastal water). 



The water was thus Polar Current water with its characteristic 

 temperature minimum at a depth of ca. 75 m. and increasing salinity 

 from surface to bottom. 



How the conditions varied from time to time, however, can be 

 seen from PI. XX, which shows all the series taken at Maroussia from 

 September 1906— July 1908, and from PI. XVIII and XIX, which' 

 show that the salinity and temperature could be different at exactly 

 the same spot within л'егу short intervals of only a few hours. The 

 changes occurring were partly those caused by the changing of the sea- 

 sons or variations in the sea and similar causes, partly those due to 

 the influence of the tides. 



The periodic, daily changes in temperature and salinity caused by the tides. 



In 1907 already I had noticed irregularities in the values for the 

 temperature and salinity from the same depth at different times of 

 the same day. A number of investigations were undertaken to test 

 the matter (series XXII, XXVI, XXVII and XXVIII, XXXI and 

 XXXII), but without result. The changes were small and irregular. 



In 1908 the investigations were continued and it proved, that 

 these changes stood in connection with the tides. 



Owing to the ice conditions the investigations in 1908 could not 

 be carried out at the usual station at Maroussia, but were made ca. 

 1 km. further north in the deep channel in Øresund. Samples for the 

 determination of the temperature and salinity were taken here every 

 hour at a depth of 100 m. throughout four changes of the tide (Series 

 LXIV, A. B, C, D), The results are shown on PI. XVIII. (At the 

 same time measurements were made of the velocity of the surface 

 current and tidal measurements were made at Maroussia (see Tab. 12)). 



The samples were taken at a depth of 100 m., the increase in 

 temperature and salinity per meter being greatest at this depth, and 



