The large spool can be had at any dry-goods store where braids or fancy cords are kept. It should be about four inches long, three inches in diameter, and with sides thick enough to enable screws to be driven into it without fear of splitting the wood. An old clock-spring is attached at one side of the spool, while at the other two circular bands of brass are made fast, one within the other. An axle of stout wire should be driven through the spool; but if the hole is too large, wooden plugs may be glued in at each end so that a front view of the spool will appear as shown at A. The metal bands are cut with shears from sheet-brass, and are attached with fine steel nails, the heads of which are driven in flush with the wood. A hole is made in the side of the spool, close beside each band, so that the ends of wires may be brought through them and attached to the bands. This arrangement is illustrated at B, and at C the opposite end is shown, with its clock-spring, one end of which is made fast to the side of the spool and the other to the cross-rail. A small round piece of wood is slipped over the axle, at the spring side, and projects a quarter of an inch beyond the spring. This is to keep the spring away from the arm that stands out on that side to hold the spool in place. [Illustration: FIG. 14 A DINING-TABLE CALL] About half an inch of space is left between the spool and the arm at the opposite side, so that the spring contact-strips may be made fast to the arm and still have room to act. A view looking down on the spool and springs is shown at D, and E illustrates the arrangement of the circular strips and the spring contact-strips. If the table is to remain permanently in the same position, only one spool will be required, for the floor wires can come up and connect directly with the contact-strips. But if the table is to be moved about, a tension-spool, independent of the push-button wires, is necessary so that the position of the table may be changed without unwinding the large spool and dropping the cords down to the floor. The smaller spool is made and mounted in the same manner, and should be placed close to the large one. But a lighter spring will operate it. One end of a double wire-cord is made fast to binding-posts, mounted on a yoke of hard rubber or fibre, so that the terminals will be kept apart, as shown at F. The other ends are passed through the holes at one side of the small spool and soldered fast to the circular strips, or a small screw may be passed down through the hole, binding the wire and touching the edge of one strip. Take care that it does not touch the other strip. The cord is then wound on the spool, and it is slipped in place so that the loose end of the spring is caught and held over a nail or screw-head. Turn the spool over several times to partially wind the spring; then attach the terminals to the wires that come up from the floor and the tension of the spring will draw the wires taut.