Fig. 10 above shows connection of the large demonstration high frequency coil, together with the size of high voltage condenser plates, arrangement of the spark gap, kick-back preventer, etc.

An experiment showing the action of the A. C. transformer and which can be performed with high frequency currents, is shown at Fig. 11 above. Two coils of wire about 24" in diameter, are constructed with the number of turns indicated in the diagram. When the primary is connected to the condenser and the spark gap, as shown, the 110 volt 16 C. P. or a 40 watt lamp connected to the secondary, will light up even when the primary and secondary coils are separated a distance of 1 foot or more, depending upon the size of the transformer or spark coil used for the exciter.

The secondary winding comprises one layer of No. 27 copper magnet wire, and two wires are wound on side by side with the two stock spools placed side by side on the floor. After the layer is completed, one of the wires is removed, leaving a properly spaced layer of wire with the turns the thickness of the wire apart, which is necessary in order to enable the apparatus to stand up under the terrific high voltage strains imposed upon it.

A separate tuning coil composed of several turns of heavy copper wire is connected in series with the primary of the Oudin, and by adjusting this inductance and the size of the condenser very fine tuning of the complete outfit can be readily obtained, finer than in any other way.

The high tension condenser for this large Oudin coil as employed by Dr. Strong in his lectures, was built up from 8" x 10" glass photo negatives, with tinfoil or thin metal leaves 1 1/2" smaller all around than the glass.

All high frequency sets, even those operating on transformers as small as 1/2 K. W. should be connected up with a kick-back preventer in the primary circuit, as shown in Fig. 10, this apparatus comprising simply two 1/2 micro-farad condensers joined in series and their central connection joined to a good ground, such as a water pipe. An additional protection on the kick-back preventer is sometimes used in the form of two needle spark gaps, about .01" long, the spark gaps being connected across each of the condensers shown.

High Frequency Experiments

An experiment showing the action of the A. C. transformer, and which can be performed with high frequency currents, is shown at Fig. 11. Two coils of wire about 24" in diameter, are constructed with the number of turns indicated in the diagram, i. e., about eight turns of No. 12 rubber covered wire for the primary, and about five turns of No. 16 rubber covered wire for the secondary. The convolutions composing each coil are tied together with tape or string at intervals.

When the primary is connected to the condenser and the spark gap, as shown, the 110 volt 16 C. P. or a 40 watt lamp connected to the secondary, will light up even when the primary and secondary coils are separated a distance of one foot or more, depending upon the size of the transformer or spark coil used for the exciter.

Many spectacular and novel experiments can be performed with high frequency currents in connection with incandescent lamps of the gas filled type, some of these lamps now being filled with neon gas, so that some very beautiful color effects are obtained with the lamps containing different gases. Radium paint and certain other mixtures present a fine opportunity for the devising of new experiments. Two or more bare copper wires may be stretched across a room and when connected to a large Oudin coil, such as the large conical coil described in the present article, will glow with a fine corona discharge in the dark, the degree of effluvium being governed by the tuning of the primary circuit, with the auxiliary inductance shown in Fig. 10. With the large conical Oudin coil another unusual experiment is to suspend an inverted umbrella from the ceiling and connect the metal frame to the ball terminal of the Oudin with a length of wire. The umbrella will glow in the dark, particularly if wetted, when a beautiful corona will spread out all around it.

End

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