156 MEASUREMENTS O\ THE ELECTRICAL CONDUCTIVITY 



arms of the tube, as well as the metal disc at the top of AB, 

 are graduated ; AB in half millimeters and CD in millimeters. 

 One complete turn of the larger electrode raises it 0.45mm., 

 and since the metal disc at the top is divided into 100 parts, 

 it is possible to read a change in the height of the electrode to 

 a few 45/10000mm. The narrow arm of this resistance tube 

 is used for measuring very high resistances, while the wider 

 arm is used for smaller. By placing the unknown resistance 

 behind the measuring resistance, or in shunt with it, it is 

 possible to measure resistances varying from one hundred 

 to thirty million ohms, within a few per cent. 



FIG. 2. 



