THE MEASUREMENT OF RESISTANCE 



169 



For field work, portable bridges are used. One design is 

 shown in Fig. 95. The carrying case contains the bridge pro- 

 per, the galvanometer, which is of the D'Arsonval type, and a 



J-'i<;. ( .)2. Whentstonc bridgr with dial arrangement of rheostat coils. 



FIG. 93. Wheatstone bridge with Schpne ratio coils and stiding-dial 

 rheostat coils. 



few cells of dry battery. In the example here shown the decade 

 arrangement with sliding contacts is adopted. 



