A diagram of the wiring is shown in Fig. 29, and in Fig. 30 the mode of attaching the ends of the coil wires to the commutators is indicated. Two complete coils of wire must be made about each channel of the armature, as illustrated on the drum of Fig. 30. These are separated by a strip of cardboard dipped in paraffine and placed at the centre of a channel while the winding is going on. In some armatures the coils are laid one over the other; but with this construction, and in the case of a short-circuit, a broken wire, or a burn-out, it is impossible to reach the under coil without removing the good one. Begin by attaching one end of the fine insulated wire to commutator No. 1; then half fill the channel, winding the wire about the armature, as indicated in Fig. 30. When the required number of turns has been made, carry the end around the screw in commutator No. 2, baring the wire to insure perfect contact when caught under the screw-head. From No. 2 carry the wire around through the channel at right angles to the first one, and after half filling it bring the end out to commutator No. 3. Carry the wire in again and fill up the other half of the first channel, and bring the end out to commutator No. 4. Fill up the remaining half of the second channel; then attach the final end to commutator No. 1, and the armature winding will be complete without having once broken the strand of wire. To keep the coils of wire in place, and to prevent them from flying out, under the centrifugal force of high speed, it would be well to bind the middle of the armature with wires or adhesive tape. After driving down the small screws over the leading-in and leading-out wires the armature will be ready to mount in the bearings. As the blocks that support the brushes and binding-posts partly close the opening to the cavity at the front, the armature will have to be inserted from the back into the strip (G) in Fig. 21. Then the back strip (D) is screwed in place. The armature, when properly mounted, should revolve freely and easily within the field-lugs without friction, and the lugs must by no means touch the armature. From thin spring-copper brushes may be cut and mounted on the block under the binding-posts, so that one will rest on top of the commutators while the other presses up against the underside. The wiring is then to be placed on the field-magnets. This is carried out as described for the electric magnets on pages 54-58 of chapter iv., each core receiving five or seven layers, or as much as it will hold without overlapping the lug or yoke. The ends of the wires are connected as shown at Fig. 14 or Fig. 15, the ends being carried down through the base and up again in the right location to meet the foot of a binding-post. The complete dynamo will appear as shown in Fig. 28.