400 SECOND INTERNATIONAL CONFERENCE, 



§ 6. Preliminary determinations of the salinity may be made on 

 board ship with appropriate instruments, but the exact determinations 

 of the salinity and density of water samples shall take place in a 

 scientific laboratory on shore. The ratios between Salinity, Density, 

 and Chlorine, given in Dr. Martin Knudsen's Hydrographic Tables, are 

 to be adopted, and the salinity is to be calculated by the use of these 

 Tables from the determinations of chlorine, or from the specific gravity. 



§ 7. At certain depths at the points mentioned in II. and elsewhere 

 on the surface, v\rater samples should be collected for analysis of the 

 gas-contents (oxygen, nitrogen, and carbonic acid). 



IV. 



§ 8. 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 meridian of Greenwich, 

 and horizontal distances are to be expressed in sea miles ( = 1,852 metres). 



§ 9. Thermometers to be used for the determination of the surface 

 temperature may be either centigrade or Fahrenheit, but for publication 

 all numbers are to be reduced to centigrade. 



In the centigrade thermometers for observation of surface tempera- 

 tures, the distance between two degree marks should be at least 5 mm., 

 and the degree be divided into at least two parts, the Fahrenheit ther- 

 mometer to be divided in a corresponding manner. 



The use of an insulated water-bottle on Pettersson's principle is re- 

 commended for moderate depths, and the thermometers used for this 

 apparatus should have a space of at least 10 mm. between the marks 

 of one degree, and the degree should be divided into 10 parts. 



For greater depths of the ocean, reversing or other similar thermo- 

 meters should be used. 



The glass to be used for the thermometers should be tested and ap- 

 proved, and the thermometers periodically verified by the Central 

 Bureau (see C. III. § 12). 



i^ 10. For the determination of salinity and density, either chemical 

 or physical methods may be adopted, provided that the salinity can be 

 determined with an accuracy of 0,o5 in a thousand parts (and the density 



up to O.OOOOi). 



The determination of these constants can be founded either upon 

 chemical analysis of the halogen by weighing or titration, or upon 

 physical determination of the specific gravity by means of the hydro- 

 static balance, pycnometer, and hydrometer, provided that measures be 

 taken to exclude disturbances arising from thermal effects, capillarity, 

 viscosity, etc. 



