In order to make a figure-eight out of the track, a crossing, or "cross-over," as it is sometimes called, will be required. This is shown in Figure 275. A cross-over permits two tracks to cross each other without interference. It consists of a wooden base, eight inches square and three-eighths of an inch thick. Four saw-cuts, each pair exactly parallel, and two inches apart, are made at right angles to each other across the top surface of the base, as shown in the illustration. The track used on the cross-over is semi-hard hoop-brass, one-half of an inch wide and of the same gauge as the steel track. The brass is more easily bent than the steel and is used for that reason, it being practically impossible to bend the steel track at right angles without snapping it. Four pieces of the brass, each five inches long, are bent at right angles exactly in the center. Four short pieces, each one and one-half inches long, will also be required. [Illustration: Fig. 276.—The Completed Cross-over.] The cross-over is assembled as shown in Figure 276. The strips marked _D_ are strips of very thin sheet-brass or copper. The purpose of these strips is to connect the ends of the track on the cross-over to the ends of the track forming the figure-eight so that the cross-over will not be a "dead" section, that is, a section of track where the car cannot get any current. The long strips, bent at right angles to each other and marked _A_, _A_, _B_, _B_, in the illustration, are forced into the saw-cuts in the base over the strips marked _D_. The small pieces, _C_, _C_, _C_, _C_, are placed in between the long strips, leaving a space between so that the flanges of the car wheels can pass. The pieces, _C_, _C_, _C_, _C_, should form a square open at the corners. The two long strips, _A_, _A_, should be at opposite corners diagonally across the square. _B_ and _B_ should occupy the same relative position at the other corners. _A_ and _A_ are connected together and _B_ and _B_ are connected together by wires passing on the under side of the base. The ends of the track forming the figure-eight are forced into the saw-cuts at the edges of the base so that they form a good electrical connection with the small strips marked _D_. It is quite necessary to use care in arranging a figure-eight track, or there will be danger of short-circuiting the batteries. The outside rails of the figure-eight, distinguished by the letter _B_ in the illustration, should be connected together by the cross-over. The inside rails, marked _A_, should also be connected together by the cross-over. In order to make a good mechanical and electrical connection between the ends of the rails when two or more sections of track are used in laying out the system, it is necessary to either solder the rails together or else use a connector such as that shown in Figure 277.