_Apparatus._ A No. 30 German-silver wire, G-S W, a little over two meters long, un-insulated (No. 81); the two-fluid cell, 2-F C (Exp. 113); galvanoscope, G V (No. 58); plate binding-posts, X, Y and Z (No. 83-84-85); copper washers (No. 87). _Arrange_ as in Fig. 96, so that the current will flow, at first, as shown by the arrow. The metal plates, M P 1 and M P 2, are used so that the connections may be changed without disturbing G V. The binding-posts may be fastened directly to the top of the table; but it will be more convenient to permanently fix them to a board, B, as shown, so that the same arrangement can be used for future experiments. The binding-posts, X and Y, should be about 1/8 in. apart, just far enough so that their edges do not touch each other. The binding-post, Z, should be fastened to B with its inside end 1 meter(100 centimeters, cm.) from the ends of X and Y. Marks should be made upon B, 10 centimeters apart, as indicated by the cross lines. This distance may be taken from the scale on the rule (No. 88). Fasten one end of the No. 30 wire, G-S W, to X. To do this twist its end around the screw, S, between X and the copper washer, then turn the screw in with a screw-driver until it firmly holds X to the board. Pass the wire around the screw in Z, and bring its free end to the other binding-post, Y, to be fastened (Fig. 96). Two meters of wire then form a path for the current from X to Y. Have the board wide enough so that another set of binding-posts can be put by the side of Y. It will be best to permanently leave the No. 30 wire upon the board, and to fasten the No. 28 wire (next experiment) to another set of binding-posts, placed in the same manner as those in Fig. 96. Make holes in the wood with an awl before forcing in the screws. =315. Note.= This experiment is usually done with a reverser in the circuit, first taking readings with the current passing in one direction, and then in the opposite direction. Considerable time will be saved by taking all the readings for one direction of the current at a time, simply using different lengths of German-silver wire, and allowing the current to flow constantly during each part. This obviates all danger of poor contacts in the reverser, etc.; it saves the trouble of handling the reverser, and much of the time needed for the needle to come to rest. [Illustration: