CHRISTIANIA, 1901. 399 



the same determined lines in the four typical seasons, so that the middle 

 of the period of working shall be in the first half of February, May, 

 August, and November respectively. The Central Council shall decide 

 how much variation in the date of the seasonal cruises is permissible, 

 having regard to the natural conditions of the different regions in which 

 researches are to be carried out. 



III. 



The observations referred to in II. would consist of : — 



§ 3. Observations of temperature, humidity, and pressure of the air 

 every two hours. Assmann's aspiration thermometer should be used, 

 and self-registering instruments (thermometer and barometer) for 

 interpolation. 



Opportunities on board the ships should be afforded to the meteoro- 

 logical offices to make physical observations on the higher levels of 

 the atmosphere by means of kites. 



The other meteorological observations are to be carried out according 

 to the methods adopted by the meteorological offices of the nations 

 represented. 



The observations, meteorological as well as hydrographical, made on 

 board the special steamers at the time of the survey in the typical 

 mouths, are to be immediately worked out under the supervision of the 

 Central Bureau (see C) for publication in a Bulletin, wherein the con- 

 ditions of the sea and the atmosphere are to be represented by tables 

 and synoptic charts in co-operation with the meteorological institutes 

 of the nations represented. 



§ 4. The temperature of the surface water shall be taken every two 

 hours or, when necessary, more frequently. It is desirable that self- 

 registering apparatus should be used for interpolation. 



Observations on the vertical distribution of temperature are to be 

 taken at the points mentioned in II., and should be taken regularly at 

 intervals of 0, 5, 10, 15, 20, 30, 40, 50, 75, 100, 150, 200, 250, 300, 400 

 metres, and so on ; but all critical parts of the curve must be determined 

 by extra readings. 



The bottom temperature is to be investigated with all possible care. 



§ 5. At every point and from every depth where the temperature is 

 observed, a sample of water shall be collected for the determination of 

 its salinity and density. 



By salinity is to be understood the total weight in grammes of the 

 solid matter dissolved in 1,000 grammes of water. 



By density is to be understood the weight in grammes of 1 cubic 

 centimetre of water of the temperature in situ t°, i.e. the specific gravity 

 in situ referred to pure water of -f- 4° C. (= S~). 



