means more difficult work on the tramway and cars, for the car must have a movable axle in order to be able to round the curve. But with a straight track the play of the wheel upon the hub should allow enough freedom of motion to overcome the little inaccuracy which may occur in the rails. Experiment will teach you just what is needed. I cannot give exact rules, because the material and location will differ with each builder, and I have found that when I give positive rules, the rules are followed, even when the material and location are entirely unsuited to the directions given. For this reason it is best for each boy to experiment for himself. Erect the Uprights first, and brace them with the diagonal boards, as shown in the diagram (Fig. 135). When you are certain the structure is firm and can stand the strain and weight of a loaded car, lay the two-by-four rails upon the ground, and fit them to the car-wheels by pushing the car over them, to see that they are just the right distance apart. If you make your track too wide the car-wheels will slip off the rails and run between them, and if you lay your track with too narrow a gauge the rails will pinch the flanges of the wheels so tightly that the car will stop, or the rails spread. When one section of the track is laid and it is found that the car runs freely upon it, nail cross-ties of ordinary boards across from rail to rail, like a ladder. Then take the ladder, and turning it over so that the rails are on top (Fig. 136), adjust it to the tramway (Fig. 135), and fasten it securely, by nailing the cross-ties to the side-boards of the tramway. In Fig. 135 The Cross-ties, or Sleepers, are put in position, to show how they will look when the track is laid, but in reality the cross-ties must be nailed to the rails while the latter are upon the level ground, as I have already stated. When each section of track is fastened in place, from the top of the tramway to the ground, and as much farther as your space or lumber will admit, load your car with stones, or some equally heavy freight, and start it down the “switchback.” If the car reaches its journey’s end with no mishap, you can with safety get in the car for the next trip and coast down yourself and a jolly good coast it will be. The plans (Figs. 135 and 136) may be altered so that the car will run down one hill and mount another not quite so high, and many other improvements will suggest themselves to the young civil engineers who build this “switchback,” but the first track you erect should be as simple as is consistent with strength and safety, and the improvements left to some future time. Ticket-Chopper’s Box. You may then take a square box, with a lock and key attached, and bore a hole in one end large enough to admit a good-sized marble; use this as the railroad and ferry-men use a ticket-chopper’s box, let every boy who wants a ride drop a marble in the box.