_Apparatus._ Same as in Exp. 125; the two-ohm resistance coil, R C (No. 79); a coil of wire, X, as, for example, the 15-turn coil on the galvanoscope, G V (No. 58). _Arrange_ as in Fig. 105. You will observe that the central conductor of the bridge (2, Fig. 104) takes the place of M P in previous explanations. We still have the same kind of a divided circuit as explained in Exp. 125, A G being connected with points of equal potential. It will be found convenient to have D C at the right, and A G facing you at the left, the key being in front. (See Exp. 107 in regard to adjusting A G.) Notice that you have a standard resistance (2 ohms) in place of R, Fig. 102, and an unknown resistance (galvanoscope coil) in place of X. (See § 330.) =329. Directions.= (A) Touch the free end of wire, 3, to the left-hand side of the bridge-wire, press the key for an instant, only, and note the direction taken by the right-hand end of the needle. Move the end of wire, 3, to the right-hand side of the bridge-wire, touch key, watching needle. Does the needle move more or less than before? In the same or opposite direction? If the deflections are opposite, the point that has the same potential as binding-post, 2, must be _between_ the two points touched. (B) Be sure that all connections are good. Find the point on G-s W, at which there is no deflection, as directed in Exp. 125 (C). Note the readings on the scale, as explained in § 324. (C) Make the proper calculation, § 327, 328, and find the resistance of the coil of G V, the resistances of the wires joining R C and G V to the bridge being neglected. (D) Make proper allowances for the resistances of the wires just mentioned (see § 330), and compare them with the results found in part (C). =330. Allowances for connections.= It should be remembered that the wires joining R C and G V to the bridge also have some resistance. Such connections, in regular instruments, are made by heavy copper straps or by thick, short wires, so that their resistances can be neglected. In case you use the ordinary No. 24 copper wire, as directed, the resistances of the pieces can be measured by means of the bridge, or you can calculate their resistances from the wire tables. The resistances should be allowed for. It is evident that your standard resistance is 2 ohms _plus_ the resistance of the connecting wires, and that the resistance of the coil, X, is found by deducting the resistance of its connecting wires from that found from the proportion previously used.