BJ0RN HELLAND-HANSEN 



[rep. of the "MICHAEL SARS" NORTH 



distribution of temperature and salinity in the central part 

 of the North Atlantic with its various currents, together 

 with some special investigations, which would fit in with the 

 route and time. Current measurements were to be made, 

 if possible, in the open ocean, especially in order to study 

 the variations of ocean currents vertically and the existence 

 or non-existence of tidal currents over great depths. Such 

 measurements were also to be made in the Straits of 

 Gibraltar. A photometer was constructed for making 

 observations, down to great depths, of the penetration of 

 light-rays of different wave-lengths. By a special agreement 

 with the authorities of the Scottish marine researches it was 

 decided that continuous observations during 24 hours, of 

 possible vertical variations in temperature and salinity should 

 be made in the Faeroe-Shetland Channel simultaneously from 

 the "Michael Sars" and the Scottish research steamer. 



The route of the "Michael Sars" is shown in the 

 chart p. 64'--. The route covered great areas where 

 previously only a few or no observations had been made 

 by modern methods. The investigations embraced: — 

 the eastern part of the North Atlantic where e. g. the 

 influence of the Mediterranean could be studied; — the 

 outskirts of the Sargasso Sea; — different parts of the 

 "Gulf Stream"; — the Newfoundland Bank with the 

 Labrador Current; — the areas on both sides of the 

 Wyville Thomson ridge. It would thus be possible, in a 

 comparatively short space of time, to make a general 

 survey of the North Atlantic with essentially different 

 characteristics. 



The demand of simultaneity can, of course, never be 

 fully satisfied by investigations with one vessel only. The 



"Michael Sars" observations were made between the 

 beginning of April and the middle of August, 1910. The 

 physical conditions at intermediate and at great depths 

 have probably not altered much during these 4 months 

 and may, therefore, be directly comparable for the whole 

 area of investigation. In the upper strata, however, the 

 seasonal variations make a direct combination of the 

 observations from different parts of the cruise very doubtful 

 or even erroneous (cf. Chapter IV). 



The observations are published in the Tables I a 

 and b, II, and V. The methods used will be described 

 and further particulars mentioned in subsequent chapters.— 



On the starboard side of the ship there were two 

 steam-winches for the hydrographic work and the work 

 with vertical nets for catching small plankton organisms. 

 The foremost winch could be coupled to a big drum and 

 to a Lucas sounding macliine. The drum was provided 

 with 5000 m. steel-wire of 3-5 mm. diam., which was 

 used for all hydrographic observations below 2000 m., 

 and also, occasionally, for observations in the upper strata. 

 The other winch was placed amidships and could be 

 coupled to two drums, one of which was used for the 

 hydrographic work at by far the greater number of stations. 

 It was provided with 2000 m. steel-wire of 2-5 mm. diam. 

 The wire was new, and very good to begin with, but after 

 a time it became corroded and worn through constant 

 use in sea-water at relatively high temperatures. Ultimately 

 parts of the wire had to be condemned. Under such 

 circumstances wire of phosphor-bronze is much to be 

 preferred; it will prove cheaper in the long run. 



11. THE SEA-SURFACE AND THE AIR. 



3. The Surface Observations. 



The surface observations were made in the ordinary 

 simple way: water was hawled up in a bucket, the 

 temperature was read, and a glass-bottle filled with a 

 water-sample for titration. The thermometers were divided 

 in 710° C. They were so sensitive that they gave the 

 temperature correct within 0-1° C in about half a minute. 

 The sample-bottles and the titrations will be mentioned 

 in section 14. 



During the greater part of the cruise the surface- 

 temperature was observed every hour, while water-samples 

 were, as a rule, only taken every second hour. Most of 

 these observations on board were made by the ship's 

 officers G. Wilhelmsen and K. Knudsen. 



4. Meteorological Observations. 



On the top of the pilot-house of the "Michael Sars" 

 we had a screen for meteorological instruments, of the 

 type generally called the Norwegian Screen. Its sides 

 were open enough to permit the air passing through them, 

 while neither direct sunshine nor rain or spray from the 

 sea could reach the instruments. The screen was placed 

 about 4 metres in front of the funnel; the instruments 

 had a height above sea-level of 5 metres. 



A psychrometer stand with dry and wet-bulb ther- 

 mometers was placed in the screen. From June 3rd to the 

 end of the cruise the thermometers were read by the officers, 

 as a rule every second hour. The air temperature was 

 also sometimes observed by means of a swing-thermometer; 



