the cell. The plan presupinises that there will be kept on board one or inoie 

 lots of sea water, the salinity of which will ha\'e been determined by some 

 other method, and that these will be used at more or less frequent intervals 

 for the purpose of standardization of the apparatus. 



GENERAL DESCRIPTION 



A simplified illustration of the bridye circuit is shown in Diagram No. I 

 Here X represents the arm of the bridge containing tlie cell in whicli tho 

 sea water whose conductivity of salinity is to be measured is placed. Y 

 represents the resistance of the cell containing other sea water whose con- 

 ductivity need not be known. Q is an adjustable resistance in the same aiin 

 of the bridge as Y. M and X are the resistances of the remaining arms of 

 the bridge when the contact <>n the slide wire is set at zero. 



AC. se'»e»ATof< 



PJAg ram N * 1- 



Readings of the apparatus ai-e to l)e converted to salinities l)y means of a 

 table or curve. 



Tlie test current i.s supplied by means of a microphone hummer, and a set 

 of head telephones serve for indicating when the bridge is balanced. A 

 thermostatically controlled water bath serves for keeping the cells at a con- 

 stant known temperature during measurement. 



THE MEASURING CIRCUIT 



The arrangement is a simple Wlieatstone bridge with what is sometimes 

 called a third branch and an inductive coupling between the current leads and 

 the detector leads. There is also a metallic shield. The arrangement of the 

 circuit, except for this shield, is shown in Diagram No. 2. The test circuit 

 is insulated from the power circuit. It is also insulated from the shield 

 except for a single connection on the tliird branch of the bridge. 



