Maxwell's Method of Comparing an Electrostatic Capacity with a Self-Inductance
J. A. G. Shirk · Transactions of the Kansas Academy of Science · 1911
If three of these resistances are known, the fourth may be determined by adjusting the three known ones until there is a balance, and hence no deflection of the galvanometer, as the points A and B will be at the same potential. This is the ordinary application of the Wheatstone bridge in measuring the resistance of an unknown conductor. If alternating currents are used there is a balance if the impedances of the four arms are proportional. The impedances consist of the resistances and reactances of the different branches. Let RI, R2, R3, and R4 represent the resistances of the four arms, as before, and let X1, X2, X3, and X4 represent the reactances of the corresponding arms. Then the impedances of the four arms become: RI-jX1, R2-jX2, R3-jXS, and R4 -jX4, where j= #-1. (This method of representing the impedances of a circuit may be found in chapter V, vol. II, of the Elements of Electrical Engineering, by Franklin and Esty.) If three of the impedances are known, the fourth can be determined by adjusting the three known ones until there is a balance in the bridge. In order to accomplish this result arrange the bridge as in figure 2. For the direct current use a storage coil or a primary battery, the current being reduced to the desired value