216. Adjustment. The part, F, and the screw, E, must be just high enough to keep L from striking the poles of M. If F is too weak, it will bend down to M. If F is too strong, it will take too much battery power to run it. In case there is not strength enough in F to quickly raise L when the current ceases to pass, arrange a screw-eye and rubber band as shown in Fig. 96. I should be slowly turned one way or the other, until it touches F just right to allow L to vibrate back and forth rapidly.
217. Operation. We shall suppose that you have all parts adjusted and the battery wires joined to Y and Z. If the current enters at Z, it will fly around through the coils, through G, F, up I, through the T-shaped tin and out at Y. The current was in L, but it could not get out at any other place than at Y. As soon as the bolts were magnetized, L was forcibly drawn down, pulling F away from I, thus opening the circuit. As the bolts were no longer magnets, F sprang right back to I, the current passed long enough to re-magnetize the bolts. This operation was rapidly repeated.
218. Use. If you wish to use the buzzer simply to call some one occasionally, a dry battery or Leclanché cell is best. This apparatus is good to work a gravity cell when it needs regulating.
Fig. 101.
219. Electric Bell. Fig. 101. Before making this bell, carefully read the directions and explanations given for the electric buzzer, [App. 125]. The parts are very much alike in the two instruments, and most of the lettering of them has been made the same in the illustrations. If you look at Fig. 101 from the side, with the letters M and Q at the bottom, you will see that this bell is merely a modified form of [App. 125].
The Base is 7 × 5 × ½ in. To the upper end of this is nailed the cross piece, D. To D are fastened the binding-posts.
The Parts, F, G, H, I, J, K, L, M, N, P, Q, are the same as explained in [App. 121] and [125].