254 



ELECTRICAL MEASUREMENTS 



aluminum needle, made in the form of a portion of a cylinder. 

 The " quadrants" are portions of two cylinders, concentric with 

 the needle. The needle is drawn into the space between them by 





Deflectione 



FIG. 138. Low-range electrostatic voltmeter and the calibration curve. 

 Damping magnet not used in this instrument. 



the electrostatic attraction. The controlling force is given by 

 a flat strip suspension and the zero may be set by means of a 

 tangent screw. 



FIG. 139. Electrostatic voltmeter for -itchboard work. 



In order to damp the instrument; the needle, which from its 

 construction forms a closed loop, is frequently arranged to turn 

 between the poles of a permanent magnet. 



