274 



ELECTRICAL MEASUREMENTS 



of the same pitch as the winding on the cylinder. The slider, 

 which is always in contact with the wire, is carried by the hood, 

 which at its lower edge has 100 graduations; fractions of a turn 

 can then be read. The whole turns correspond to the divisions 

 on the vertical scale seen at the front in the upper figure. 



FIG. 156. Leeds and Northrup potentiometer. 



The resistance of each of the 15 coils which are in series with 

 the slide wire, shown between D and A, is 5 ohms. The standard 

 potentiometer current is 1/50 amp., thus making the drop in 

 each coil and in the slide wire 0.1 volt and the total drop from 



