Box Bridge

A constriction of Wheat stone's Bridge in which the nece ary resistance coils are contained in a single box with plugs for throwing the coils in and out of circuit, and connections to bring the coils into the different arms of the system. The cut shows a box bridge. Connections for the galvanometer, battery wires, and terminals of the unknown resistance are provided, by which its resistances and the connections are brought into the exact relations indicated in the conventional diagram of Wheat stone's bridge. (See Wheat stone's Bridge.) Referring to the cut, the battery wire, say from the zinc plate, connects at A1, thereby reaching A, its true connecting point. To B1 one end of the galvanometer circuit or lead is attached, thereby reaching B, its true connecting point. To C are connected the other end from the galvanometer and one end of the unknown resistance. The other end of the unknown resistance, and the other end of the battery wire, in this case from the carbon plate, connect to D. At G is an infinity plug, as it is called. When out it breaks the circuit. In use after the connections are made the key is depre ed and the galvanometer observed. The resistance is changed until no action of the resistances of the arms gives the proportion for calculating the unknown resistances. Synonym--Commercial Wheat stone Bridge, or commercial form of same. IMG:8956969607833025625_086F65.jpg: Fig. 65. TOP OF BOX BRIDGE. 86   STANDARD ELECTRICAL DICTIONARY.