=No. 80.= A Wheatstone's bridge (Fig. 103), including a scale (No. 100). The aluminum straps, 1, 2, 3, are fastened to a neat wooden base, 10 in. long by 2 in. wide. A No. 28 German-silver wire is used for the bridge. =No. 81.= A piece of No. 30 uncovered German-silver wire, 2.1 meters long, used for resistance (Fig. 96). =No. 82.= A piece of No. 28 uncovered German-silver wire, 2.1 meters long. =No. 83-85.= Three plate binding-posts, consisting of bent straps of sheet aluminum (X, Y, Z, Fig. 96). =No. 86.= Two ounces of copper sulphate, commonly called bluestone. The crystals may be kept in a large wooden pill box. =No. 87.= One dozen copper washers. =No. 88.= One combination rule, 1 ft. long, marked with English and metric systems. =No. 89.= A hollow coil of No. 24 insulated copper wire (Fig. 130). The spool, on which the wire is wound, has a hole for a five-sixteenths inch core. It is turned down thin, so that the wire is near the core. The coil is about 1-1/8 in. long and 1 in. in diameter. Spring connectors are joined to the ends of the coil. =No. 90.= A hollow coil of No. 25 insulated copper wire, similar to No. 89, with spring connectors attached to its ends. =No. 91.= Carbon rod for electroplating. =No. 92, 93.= Two soft iron cores, with screws (I C, Fig. 130). These cores are 5/16 in. in diameter, and have a threaded hole in one end for fastening them to No. 94. =No. 94.= A tin box with three holes punched in its top (Fig. 132). This serves as a base, as well as a yoke, for the two electromagnets, A, B, shown in plan. =No. 95.= Combination connecting plates (Fig. 132). Three aluminum straps are fastened to a wooden base. They are turned up at their ends so that spring connectors can be easily pushed upon them. =No. 96.= One long iron core (L I C, Fig. 140). This is of soft iron, 5/16 in. in diameter, and long enough to pass through both coils (No. 89, 90). =No. 97.= Bar magnet, about 4 in. long and 5/16 in. in diameter. =No. 98.= Coil of insulated wire wound on a soft iron core, to act as a primary coil for induction experiments. This coil fits inside of the hollow coils (Nos. 89, 90). =No. 99.= A printed degree-card for the galvanoscope (No. 58). This is printed on stiff cardboard, about 3 in. in diameter. =No. 100.= A printed scale for the Wheatstone's bridge (No. 80). This is printed on stiff paper. The scale is 8 in. long, and is divided into 10 large divisions, each of which is subdivided into 10 parts, thus making 100 parts in all. INDEX. Numbers refer to paragraphs. See Table of Contents for the various experiments. Abreast, arrangement of cells, 365. Accumulators. (See storage cells.) Action, local, 273. Air, as insulator, 144, _a_. Alternating currents, 443. Amalgamating, 257, 274. Amber, 107. Ammeter, 353. Ampere, the, 351, 357. Ampere's rule, 386. Annealing, 6. Annunciators, 471. Anode, 373, 378. Applications of electricity, Chap. XXVII. Arc lamp, 485.