Nikola Tesla: Colorado Springs Notes, 1899-1900 Page 428

November 16-20

Capacity measurements made during the period 16 - 22 November agree on the whole with those made earlier. Tesla does not explain why he repeated similar measurements, e.g. those of November 16th and 18th when he determined the distributed capacity of the supplementary coil and the vertical wire. Nor does he explain why he repeated the measurements of the change of capacity of the sphere with elevation (see November 18th and 20th). He may only have wanted to confirm the earlier results.

On November 17th and 19th he measured the capacity of a vertical wire of various lengths and gauges. From his comments on November 17th it may be seen that at greater lengths he expected some inductive effect. A check of the wavelength, however, reveals that all Tesla’s antennas were short in comparison (h/λ of the order of 0.01), so that divergence between the theoretical and measured values cannot be ascribed to an inductive effect.

November 21

For some reason which he does not explain, Tesla was interested in the capacity of the same wire when vertical and horizontal, which he measured by the usual resonance method, repeating it with a different capacitance in the primary as a check. Although the results from the two sets of measurements differ appreciably, the value obtained with the wire horizontal was somewhat higher in both cases. The formulae which Tesla used July 24th here yields 54.37 cm for the vertical wire and 58.43 cm for the horizontal. These values agree well with his measurements, especially the first set.

November 24-26

To check the values for the inductance in the primary circuit (of the oscillator) which he had earlier measured by the voltage, current and frequency method (see October 30th), Tesla repeats these measurements using the resonance method. He described the procedure on October 21st and made some measurements but did not follow them up with calculations. This time he made both measurements and calculations, but only for one L_pC_p combination. He compares them with values derived from the table given November 8th using linear interpolation. He was probably satisfied with the agreement, and did not make further checks. He had measured the capacity of the same structure, but without the protective cap and using the “extra” and “experimental” coils, on November 7th. On November 12th he had made similar measurements using the 1314-turn coil. In the 26 November entry he refers to the result of 7 November with a new “extra” coil. There is also one more result obtained with an “extra coil”, using the best method he had developed for detecting resonance (see 13 November). This result, which differs appreciably from the others, is not mentioned November 26th.

The remark closing this entry suggests the possibility of systematic error in the determination of resonance, and Tesla emphasizes that it has to be checked.

December 5

In this, as in earlier measurements, he found a “reduced inductance of the primary because of the reaction of the secondary”. This interpretation of the functioning of the oscillator diverges from Oberbeck's theory⁽²⁹⁾. If the spark duration is relatively long