Nikola Tesla Books
Books written by or about Nikola Tesla
October 29
His remark about eddy currents in the sphere is interesting. To prevent their formation he slit the tinfoil with a knife. Did he assume that in the vicinity of the coil the sphere would behave like a short-circuited turn? It is readily shown that if this effect is pronounced (and not taken into account) the measured capacity of the sphere will be too low. This might be an explanation for the reduction of the effective capacity of the sphere in the lowest position (see the calculation of October 28th for an 18" sphere in the lowest position).
October 29
It contains a new measurement series with larger sphere and somewhat changed excitation of the measurement circuit. The excitation is now regulated by an adjustable arcing gap between the lower coil L terminal and grounding (for other details of the scheme please see Oct. 23). The note related to eddy-currents on the globe is very interesting. In order to prevent the occurrence of these currents Tesla makes slits in the metal foil by knife. Did Tesla assume that the sphere in the vicinity of the coil acts like a short circuited turn or something similar? If this effect is distinct and neglected, it is easy to show that the measure value for the sphere will be smaller than actual. It is possible that this effect causes the effective globe capacitance reduction in the lowest position (please see the calculated value obtained on Oct. 28 for the sphere of 18" diameter in the lowest position.)
In some cases Tesla finds that the resonance adjustment is not sharp. By calculation he checks the coil validity factor. The actual validity factor is certainly smaller because Tesla takes the coil resistance at direct current.
October 30-31
He continues measurements, which involve the primary coil of the big high frequency transformer, regulating coil and the inductance of the connections. The wiring scheme is shown on Oct. 30; except that the short circuit is established via a rotating arcing device and a capacitor. So only the above mentioned inductances remain in the circuit. The measurement method has been explained several times so far. As a new item it is explained how the signal of the frequency of approximately 140 Hz is produced and how the frequency measurement is performed.
On Oct. 31 he determines the new coil parameters by measurement. This coil was made by rewinding the coil with 689 turns which was mentioned on Oct. 22. He takes thicker wire in order to improve the quality factor. Measured values he compared with calculated values.
