STOCKHOLM, 1899. 103 



(b) 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 the 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. 



(c) 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 one cubic 

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

 in situ referred to pure water of + 4°C ( = ^S*^). 



For orientation, preliminary determination of the salinity should be 

 made on board ship with expedient instruments, but the exact deter- 

 mination of the salinity and density of all samples shall take place in 

 a laboratory for scientific work. 



(d) At certain depths of the points mentioned in ii., and elsewhere 

 on the surface, water samples should be collected for analysis of the gas- 

 constituents (oxygen, nitrogen, and carbonic acid). 



IV. 



For measurement of depth the unit to be adopted is the metre, 

 together with which the depth may be also recorded in English fathoms. 



Geographical points are to be referred to the longitude of Green- 

 wich, and horizontal distances are to be expressed in sea-miles ( = 1,852 

 metres). 



Thermometers to be used for the determination of the surface-tem- 

 perature may be either centigrade or Fahrenheit, but for publication all 

 numbers are to be reduced to centigrade. 



In the centigrade thermometers the distance between two degree- 

 marks should be at least 5 mm. and the degree divided at least in two 

 parts, the Fahrenheit thermometer to be divided in a corresponding 

 manner. 



The use of Pettersson's insulated water-bottle is recommended for 

 moderate depths, and the thermometers used for this apparatus should 



* Units of weight are here used instead of mass-units. 



