Nikola Tesla Books
Books written by or about Nikola Tesla
over the gap are of very high frequency and the low frequency current of supply - or if it be a direct current - can not follow. The system then works economically and the economy is much greater than might be supposed judging from the unavoidable losses in the arc. As the capacity was too small a flaming arc often formed in the box, a sure sign of bad working, the curious feature being that the arc was of a decidedly red color. This may be due to the alumina which was formed as the break wheel was of aluminum. As was expected, the use of two additional gaps improved the working of the apparatus, reducing the trouble due to the short-circuiting of the Westinghouse transformer. It was observed that when the gaps were made so large that the arc did not break through, a lamp on the supply circuit near the condensers - about 6 feet from the same - would brighten up. I am not quite sure that this was due to resonant rise in the Westinghouse transformer, for it may have been due simply to electrostatic action from the jars, as I have observed a similar effect before. When the electrostatic influence is strong the gas in the bulb is excited, the discharge passing through the same though, of course, it is not visible on account of the intense light of the filament. Particles are thrown off and against the carbon and the same is, on the one hand heated to a higher temperature while on the other hand, owing to the hotter environing medium it can not give the heat away so fast as normally - hence it brightens up. Possibly also a small part of the current of supply passes through the excited gas and slightly more energy is drawn from the mains. It was evident that, as was expected, the free vibration of the coil took place more readily than before when the coil with 260 turns was used, owing to the larger momentum as before explained. The streamers were larger than with the old coil but not quite so large as it was surmised they would be. Partially because of this fact, and partially also because not enough energy could be supplied from the Westinghouse transformer to the primary, owing to the small primary capacity, it was decided to change the connection so as to get the next lower or fundamental tone in the primary, this being in all probability the true note of the coil. The capacity in the primary was made 32 jars on each side in multiple, making the total capacity 16 x 0.00334 = 0.05284 mfd.
The primary vibration was now just an octave lower than before but the results proved inferior to those first obtained. There was now only one thing possible and that is, that the tone was right after all, in the first experiment, but the results were not quite satisfactory because the primary capacity was too small, thus unfavorable for the best working of the Westinghouse transformer. Accordingly, the same vibration was again secured in the primary but this time by using a capacity four times larger and reducing the inductance to one fourth, which was done by putting the two primaries in multiple. Now, indeed, the results were satisfactory, for the Westinghouse transformer could supply much more energy, practically four times as much as before. The streamers were now much stronger, extending to a distance of 6 1/2 feet from the top of the coil and they were abundant and thick. I can not understand why they should be of such a deeply red color. Those in New York never were such. Perhaps it is due to the smaller atmospheric pressure in this locality. Their movement, and darting about is also much quicker and more explosion like. At times a big cluster of them would form and spatter irregularly in all directions. Sometimes it appeared as if a ball would form above the coil, but this may have been only an optical effect caused by many streamers passing from various points in different directions. Many times sparks passed from the top of the coil to the point where the lower end of the coil was connected to the secondary “free” terminal. These sparks were 8' - 9' long.
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July 29
To check out his theoretical conclusions about the free oscillation of the “extra coil” (see 30 June and 26 July) Tesla made a new coil with a higher inductance. As this was his first experiment with the new coil, he had to adjust the circuit parameters by trial and error.
Tesla's ingenuity found full expression in the way in which he developed condensers for high voltages. He filed a patent application on his design for a fluid electrolyte condenser on June 17th 1896(67).
July 29
For the purpose of theoretical conclusions of "additional coil", free vibrations checking (please see June 30 and July 26) Tesla constructs a new coil with higher inductance than previously. With this new ''additional coil'' he puts the oscillator in operation. As he used to do it, he weighs the inductance in primary circuit (means of regulating coil) and numcer of jars (i.e. capacitance) so as to obtain the maximum voltage in the secondary. The rough estimate of operating frequency obtained on the basis of inductance and capacitance in the primary.
When adjusting arcing device (please see July 27) he observes that the bulb on the network supply feeder gives a brighter light when there is no spark on the arcing device. He is not sure whether the reason is capacitive loading of the Westinghouse transformer (network transformer) which could cause a resonant overvoltage. He suspects "electrostatic action" and gives his opinion on that phenomenon.
During the process of looking for the conditions for best oscillator operations, Tesla checks the circuit parameters. He matches the primary capacitance according to supply transformer power. By capacitance increase in the primary he provides a larger energy transfer, but the best results are obtained when the system operates at suitable frequency. The operating system he applies here could be named "test and guessing method", which is understandable with regards to his first experiments with new "additional coil".
"Additional coil" described on June 29 was wourid on the same core as the coil which he uses now, but with approximately twice as many turns. Tesla expected that the new coil's self-resonant frequency will be approximately twn times lower. That is why, when testing the oscillator, he reduced its frequency by increasing the primary capacitance. When that didn't provide the expected results, he reduced the inductance (by connecting two primary turns in parallel instead of in series) and when he obtained good sparks, he stopped at that. From the description of the sparks some kind of enthusiasm is evident, and the writing method is such that one almost forgets that the description of a physical event is in question.
By gradually increasing the exciting network transformer voltage (he came to 22,500 V), Tesla achieved the capacitor withstand limit. The capacitor was made of glass jars. In order to avoid the numerous jars connected in series for the purpose of high voltage achievement, he tests another kind of jar with thicker walls.
When one has in mind the complexity of technical venture of capacitor production for such high voltages, the simplicity with which Tesla solved that problem is very impressive. Capacitor design with fluid electrodes, Tesla protected by patents submitted on June 17, 1897(67).
* Possible by mistake, Tesla designated both sensitive devices with A'. In text A and A' appear, and on the given drawing the correction has been made. In the original text, Tesla, talking about device sensitivity, mentioned the experiments with sensitive device A' which required the text correction with regard to the above correction.
