170 



ELECTRICAL MEASUREMENTS 



Calibration of a Resistance Box. In order that any changes 

 In the coils may be detected, all resistance boxes and Wheat- 

 stone bridges should be calibrated occasionally. A convenient 



FIG. 94. Schone arrangement of ratio coils for Wheatstone bridge. 



m LEEDS&NORTHRUP DIAL DECADE TESTING 

 TYPE S :' 



THE LEEDS &NORTHRUP CO. 



PHILADELPHIA. 



~^^^^^^^ 



FIG. 95. Portable Wheatstone bridge with sliding-dial coils. 



method of doing this with- sufficient accuracy for general labora- 

 tory work, and one for which the apparatus is readily assembled, 

 is shown in Fig. 96. It is a substitution method involving the 

 use of the bridge principle. 



