This consists of two brass spheres, generally 3 inches in diameter, and mounted on a stand or sometimes on top of the induction coil. The distance between the balls is readily adjustable by either attaching the balls on the ends of two sliding rods, or causing the balls themselves to slide on the rods (Fig. 77).
Fig. 77. Fig. 78.
Triple Oscillator.
Here three balls are used, two outside ones connected to the circuit, being one-half inch diameter, and the middle one, isolated from all connection, of three inches in diameter. This form is best mounted on a separate stand, the balls either being on glass or hard rubber legs (Fig. 78). Connecting wires from the secondary of the coil must in all cases be run with the greatest precautions against crosses, as directed in Chapter V.
It is possible to make many different designs in oscillators. Some experimenters use the simple Clarke form, others prefer the triple balls; yet, again, others vary the sizes and the relative sizes of the balls. One form of oscillator prescribes the balls to be immersed in oil or vaseline. Such methods all have their adherents. Even the plain points of an induction coil discharger will serve for short-distance work.
Oscillators are adjusted by altering their proximity to one another, and should have care given to keep the spheres bright. It is easy to alter capacity of an oscillator by connecting its spheres to other insulated spheres.
The Coil.
The coil for wireless telegraphy does not differ from the regular Ruhmkorff, except that in place of the contact breaker a signal or Morse telegraph key is substituted. Of course, the contact breaker can be made to perform the same duty by retracting the adjusting screw out of reach of the platinum on spring, and then operating the hammer and spring in same manner as key.