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Two "self-induction bobbins," L Ll, a well-known device of electricians for opposing resistance to electric waves, are included in the circuit of the Morse instrument the better to confine the action of the waves to the powder in the tube. Further, the tube d is connected to two metal conductors V Vl, which may be compared to resonators in music.
The effects of capacity are the most striking, for in these experiments, since the self-induction and frequency both are high, the critical capacity is very small, and need be but slightly varied to produce a very considerable change.
The Bell telephone, however, is extremely sensitive, and this induction affects it so much that a conversation through one wire can be overheard on a neighbouring wire. Moreover, there is such a thing as "self-induction" in a wire that is to say, a current in a wire tends to induce an opposite current in the same wire, which is practically equivalent to an increase of resistance in the wire.
Where this type of interrupter is employed the condenser that is usually shunted around the break is not necessary as the interrupter itself has a certain inherent capacitance, due to electrolytic action, and which is called its electrolytic capacitance, and this is large enough to balance the self-induction of the circuit since the greater the number of breaks per minute the smaller the capacitance required.
In operating an induction coil with rapidly alternating currents, we realize with astonishment, for the first time, the great importance of the relation of capacity, self-induction and frequency as regards the general result.
But Edison discovered that by utilizing a shunt around the receiving instrument, with a soft iron core, the self-induction would produce a momentary and instantaneous reversal of the current at the end of each impulse, and thereby give an absolutely sharp definition to each signal.
A condenser is connected across the contact points of the vibrator since this gives a much higher voltage at the ends of the secondary coil than where the coil is used without it; this is because: the self-induction of the primary coil makes the pressure of the current rise and when the contact points close the circuit again it discharges through the primary coil, and when the break takes place the current flows into the condenser instead of arcing across the contact points.
A single coil wound upon a core has a high self-induction; for this reason principally, this type of motor was chosen to perform the experiment. Were a secondary closed coil wound upon the core, it would tend to diminish the self-induction, and then it would be necessary to employ a much higher frequency and potential.
Now, if anything is desirable in this case, it is to increase the frequency, and this would make it still worse for the electro-dynamic effects. On the other hand, it is easy to exalt the electrostatic action as far as one likes by taking more turns on the secondary, or combining self-induction and capacity to raise the potential.
There is as yet no authoritative statement as to exactly what happens, and it is generally assumed that the effect depends on the relation of capacity to self-induction, and is a sort of resonator action. This would need a large self-induction, and a small change of speed would stop the effect. The following explanation is suggested.
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