─────────────────────────────────────────────────────────────────── Size of A C D E F G H Q Coil ─────────────────────────────────────────────────────────────────── 1/4 in. 8 in. 1 3 4 3 1 5/8 4 1/8 in. 7/8 in. 7/16 in. 1/4 in. in. in. in. ─────────────────────────────────────────────────────────────────── 1/2 in. 8 1/4 1 3 5 3 1 5/8 4 in. 1/8 in. 1/8 in. 7/16 in. 1/2 in. in. in. in. ─────────────────────────────────────────────────────────────────── 1 in. 10 1 3 7 4 1 5/8 6 1/4 1/4 1/2 1/8 in. 7/16 in. 1/2 in. in. in. in. in. in. ─────────────────────────────────────────────────────────────────── The condenser is fastened to the under side of the base by means of a wooden strip passing across it and secured to the base by means of two small wood screws. One of the binding posts is connected to one of the primary wires. The other primary wire is connected to the spring. The other binding post is connected to the standard. The condenser is connected directly "across" the interrupter, that is, one wire is connected to the spring and the other wire to the standard. Two binding posts are mounted on the wooden bridge and then the bridge is fastened across the top of the coil by means of two brass nails. The secondary terminals are connected to these binding posts. The Coil is now ready for operation. Connect two pieces of wire to the secondary binding posts and bring them toward each other until they almost touch. The space between should be about one-quarter of an inch long. [Illustration: FIG. 121.—Diagram of Connections.] Connect three or four good dry cells to the primary posts and turn the thumbscrew until the contact point on the end touches the contact on the spring. The interrupter should immediately commence to "buzz" and if the coil has been properly constructed and connected, a stream of sparks will jump between the wires connected to the secondary. It may be possible that the action of the interrupter and consequently the strength of the sparks at the secondary can be improved by bending the spring’ either away or towards the core. A little experimenting will soon show just how much tension the spring should have. When the proper position of the thumb-screw is found, tighten the lock nut so that it cannot change its adjustment. [Illustration: FIG. 122.—Perspective view of Coil showing names of the various parts.] Details and instructions for building and experimenting with larger spark coils are given in our books "Experimental Wireless Construction" and "Induction Coils."