Figs. 178 and 179 show, respectively, side and front views of the original Kellogg bell.  The entire mechanism is self-contained, all parts being mounted on the base plate 1.  The electromagnet is of the two-coil type, and is supported on the brackets 2 and 3.  The bracket 2 is of iron so as to afford a magnetic yoke for the field of the electromagnet, while the bracket 3 is of brass so as not to short-circuit the magnetic lines across the air-gap.  The reed tongue—­consisting of the steel spring 5, the soft-iron armature pieces 6, the auxiliary spring 7, and the tapper ball 8, all of which are riveted together, as shown in Fig. 178—­constitutes the only moving part of the bell.  The steel spring 5 is rigidly mounted in the clamping piece 9 at the upper part of the bracket 3, and the reed tongue is permitted to vibrate only by the flexibility of this spring.  The auxiliary spring 7 is much lighter than the spring 5 and has for its purpose the provision of a certain small amount of flexibility between the tapper ball and the more rigid portion of the armature formed by the iron strips 6-6.  The front ends of the magnet pole pieces extend through the bracket 3 and are there provided with square soft-iron pole pieces 10 set at right angles to the magnet cores so as to form a rather narrow air-gap in which the armature may vibrate.

[Illustration:  Fig. 178.  Under-Tuned Ringer]

The cores of the magnet and also the reed tongue are polarized by means of the =L=-shaped bar magnet 4, mounted on the iron yoke 2 at one end in such manner that its other end will lie quite close to the end of the spring 5, which, being of steel, will afford a path for the lines of force to the armature proper.  We see, therefore, that the two magnet cores are, by this permanent magnet, given one polarity, while the reed tongue itself is given the other polarity, this being exactly the condition that has already been described in connection with the regular polarized bell or ringer.

The electromagnetic action by which this reed tongue is made to vibrate is, therefore, exactly the same as that of an ordinary polarized ringer, but the difference between the two is that, in this harmonic ringer, the reed tongue will respond only to one particular rate of vibrations, while the regular polarized ringer will respond to almost any.

As shown in Fig. 178, the tapper ball strikes on the inside surface of the single gong.  The function of the auxiliary spring 7 between the ball and the main portion of the armature is to allow some resilience between the ball and the balance of the armature so as to counteract in some measure the accelerating influence of the gong on the armature.  In these bells, as already stated, the natural rate of vibration of the reed tongue was made somewhat lower than the