Nikola Tesla: Colorado Springs Notes, 1899-1900 Page 425

November 5

Photographs of the Colorado Springs laboratory always show the pole rising from the center of the building. Its dimensions are given in the entry of 17 October. Now Tesla calculates the capacity of the pole as the sum of the capacities of its parts of different thickness, using the formula first cited on October 28th. His final remark indicates that he had thoroughly understood the physical essence of the phenomenon.

November 6

Tesla carefully measured the capacitance of the aerial pole by the resonance method, from the known inductance of the 550-turn coil (see September 8th) and known frequency of the oscillator, with two measurements, one with and the other without the capacity to be measured. He did not make use of his earlier results for the inductance of the regulating coil and connections from October 30th, although he could have done. A calculation check shows that the results of October 30th were rather high (by as much as 10% for 2 1/8 turns of the regulating coil), but Tesla probably thought that the new procedure was better and so did not use the old results. An analysis shows that if the old values had been used the final result would not have been essentially affected, so that Tesla’s conclusion that the measured capacity of the pole was less than the theoretical value of November 5th remains valid.

From the relatively lengthy discussion following the measurements it may be seen that Tesla expected just the opposite. As usual when his expectations were not fulfilled, he considers ways for getting more reliable results.

November 7

Measurement of the capacity of the structure at two frequencies was intended to demonstrate the reduction of effective capacity with increasing frequency. Tesla did in fact obtain a small difference, but it is dubious proof considering the accuracy of the measurements. The frequency difference was quite large, from 50 kHz to nearly 250 kHz (using “extra” and “experimental” coils).

November 8

The primary inductance values cited are from November 5th. The other values given in the table do not agree with those derived from the measurements of October 30th. Also, earlier data do not include values for half a turn of the regulating coil. It must therefore be concluded that the measurements from which the tabulated values were calculated are not described in the diary.

It seems that in measuring inductance from voltage, current, frequency and resistance Tesla had difficulty because of unreliability of the frequency determination. He therefore used the voltage ratio, when it is only necessary for the frequency to be constant. By this method he measured the inductance of the regulating coil plus connections, for various numbers of turns.

November 9

The measurements of mutual inductance in terms of the inductance of the primary when the secondary is open and short circuited are noteworthy. They were made at constant current and frequency, simplifying the calculation.