

WHEATSTONE'S BRIDGE  LoveToKnow Article on WHEATSTONE'S BRIDGE (Site not responding. Last check: 20071018) 
  The resistance forming the four arms of the bridge can be so adjusted that if these resistances have values denoted by P, Q, R, and S, then when P: Q :: R: S, the current in the galvanometer circuit will be zero when an electromotive force is applied in the battery circuit. 
  The operation of determining the value of the resistance R therefore consists in altering the ratio of the three resistances P, Q, and S, until the galvanometer indicates no current through it when the battery circuit is completed or closed by the key. 
  In one form of Wheatstone's Bridge, known as the series pattern plugresistance bridge, or Post Office pattern, the two ratio arms, P and Q, each consist of a series of coils of wire, viz. 
 37.1911encyclopedia.org /W/WH/WHEATSTONE_S_BRIDGE.htm (684 words) 
