Nikola Tesla: Colorado Springs Notes, 1899-1900 Page 52

June 30

Description of electric circuits in terms of mechanical analogies was at one time very popular. The resonance of an electrical circuit was likened to the swinging of a pendulum, and coupled resonant circuits to two pendulums linked together⁽³⁹⁾. Maxwell and his followers even tried for a long time to describe the electromagnetic field in terms of a mechanical model⁽⁴⁰⁾. Tesla's comparison of his "additional coil" to a pendulum is not precisely formulated but rather intuitive. He correctly discriminates between the excitation (initial conditions) and the Q-factor. He does not fully explain how he imagined that the vibrations of the three systems, the primary, the secondary and the "combined system", would be the same. By "freeing" the additional coil he means a weakening of the coupling between it and the secondary exciting it. He obviously had a clear understanding that a circuit can oscillate at its own resonant frequency if the coupling with an excitation circuit is loose.

June 30

Since Tesla very frequently used Thompson equation with LC circuit without losses, he found it helpful to prepare suitable equations on the basis of which with minimal calculations he can obtain desirable values.

In continuation of the notes he sorts out the impressions and results (maybe because that is the end of the month?). Comparison of events in electrical circuits with mechanical analogous systems was in the past popular. The resonance of the electrical circuit connected with pendulum, the event in linked resonance circuits with two pendulums which are mutually linked⁽³⁹⁾.

Even Maxwell and his followers attempted for a long time to describe the electromagnetic field by means of a mechanical model⁽⁴⁰⁾. Tesla's comparison of "additional coil" with pendulum was not precisely shaped - it is more by intuition. Tesla correctly segregated the excitation (initial conditions) and quality factor. He didn't thoroughly explain how he imagined that free vibrations of three systems would be the same: primary, secondary and "combined system". When he talks about "releasing" of additional coil, he foresees the weakening of its link with the secondary which excites it. Tesla had a clear imagination that the circuit tends to vibrate on its own resonant frequency if poorly linked with the excitation. It is strange that he didn't apply this logic on the secondary circuit which he intentionally designed to be in strong link with the oscillator primary circuit.