In regular galvano-faradic machines the current regulator is formed of a hollow cylinder which is drawn from the core of the coil; but in this simple machine the water-jar regulator may be connected between a pole of the battery and the binding-posts (D or E of Fig. 11). The wires of the handles are attached to posts (A and B of Fig. 11), and when all the wires are in place and the current turned on by means of the switch, the vibrator begins to work and the shocking-current is felt through the handles. By means of the regulating-screw that bears on the armature, the number of vibrations may be increased or diminished, but for faradic purposes the vibrations should be as quick as possible. Much amusement may be had with this apparatus, and a large number of people may be given a shock by getting them to join hands when standing or sitting in a circle. An Electric Buzzer This piece of apparatus is, in theory, nothing more than the electric bell, and might properly be included in Chapter V., on Annunciators and Bells. But since it is the logical development of principles just laid down, it has been thought best to give it its present position. The electric buzzer is constructed on the principle of the telegraph-sounder, but instead of making a single click or stroke the current is made to act on the armature and keep up a continuous motion so long as the electricity passes through the helix of the cores, the armature, and the contact-points of the apparatus. A buzzer has the same movement as an electric bell with the ringing apparatus removed. For offices, houses, and quiet calls it is often preferred to the loud ringing of a bell. The electric buzzer shown in Fig. 13 is easy to make; it is operated by the aid of a cell and a push-button. Cut a base-block three inches and a half wide, five inches long, and three-quarters of an inch thick, and mount a horseshoe magnet made of bolts and a yoke and coils about at the middle of it, as shown in Fig. 9. The magnet is held to the base by a flat wooden cleat and a screw passed down through a hole in the cleat and into the base, between the coils. An armature of soft iron, two inches long and half an inch wide, is riveted to a piece of spring-brass, as shown in Fig. 14 A, and the end is bent so that it will fit around the corner of a block to which it is held fast with two screws. This armature is mounted so that there is a space one-sixteenth of an inch wide between it and the bolt-heads, as you can see in Fig. 9. The brass is bent out slightly and runs parallel with the armature for one inch and a quarter. Against this the end of the screw mounted in block B Fig. 9 rests. [Illustration: FIG. 13] [Illustration: FIG. 14]