Nikola Tesla Books
Books written by or about Nikola Tesla
Now when the ball was attached the primary capacity was
$! {{23 \over 2} \times 0.003 = {0.069 \over 2} = 0.0345} $! mfd.
and the period
T2 was $! {= {{{2 \pi \over 10^{3}} \sqrt{0.0345 \times {7 \over 10^{5}}}}} = {{2 \pi \over 10^{3}} \sqrt{2415 \over 10^{9}}} =} $!
$! {T_{2} = {{{2 \pi \over 10^{7}} \sqrt{241.5}} = {{2 \pi \over 10^{7}} \times {{2 \pi \times 15.54} \over 10^{7}}}} = {97.6 \over 10^{7}}} $! and n = 102,460 per sec.
The ball slows the vibration of the coil very much down. From a series of observation with capacities of varying value useful estimates may be made and the quantities of moment calculated. This mode of proceeding seems to offer features of considerable value in experimentation and it will be followed up. A curious observation in these experiments was that maximum rise was obtained always with the regulating coil practically all out.
How is this to be explained?
Experiments with the secondary 35 turns were resumed. The probable causes of the curious phenomenon that maximum resonant rise (on the coil attached to the terminal of the secondary, as before described) took place when the self-induction regulating coil was practically all cut out - were considered. Evidently when the coil was cut out there was more energy available for the excitation of the primary turn and therefore the secondary was more strongly energized, this giving a higher electromotive force on its terminals. Owing to this the impressed e.m.f. on the coil attached to the free terminal of secondary was greater and therefore the coil was more strongly excited. Assuming then that the secondary free vibration did not take place, this explanation would be acceptable but for one thing: the maximum rise on the coil with 260 turns did not occur, when all the turns of the primary regulating coil were cut out, but at a point when there remained still a few turns in series with the primary. The phenomenon must be therefore interpreted differently. To all appearances the secondary free vibration did occur, and there was a certain inductance in the primary which gave the highest e.m.f. on the excited coil on the free terminal of secondary. But now the latter was in fairly close inductive relation with the primary hence its own vibration was more or less modified by that of the primary. In altering the primary vibration, that of the secondary must have been, therefore, correspondingly altered. Now, the secondary excited the coil with 260 turns and, to insure the maximum rise on the free terminal of the coil, the secondary vibration ought to have been of exactly the same pitch as the free vibration of the coil. From this it is plainly seen that if the primary vibration was such as to favour a rise in the secondary of the pressure at the free terminal then the impressed e.m.f. on the coil with 260 turns was greater; but this evidently, judging from the actually observed results, took place when the secondary vibration was âout of tuneâ, more or less with the free vibration of the coil. Thus it happened that by raising the secondary e.m.f. up to a certain point there was an increased resonant rise on the excited coil. But when, by further cutting out turns of the regulating primary coil, the secondary vibration was modified more and more and brought âout of tuneâ with the free vibration of the coil excited by the secondary, the resonant rise on the terminals of the excited coil was diminished. Now, with a certain small number of turns of the regulating coil still included in the primary, the relation between these opposing elements determining the
102
July 24
During that day the notes are divided in three parts (previous day in two parts), which is shown by designation of original handwritten pages. The first part pertains to experiments with oscillator secondary with 35 turns, and it is described on three pages; second part on five pages, pertains to this experiments continuation, and third part on three pages is devoted to the question of oscillator secondary capacitance. The oscillator secondary consists of 35 turns.
When adjusting the oscillator; Tesla most frequently changes the regulating coil in the primary, and so obtains the maximum voltage in secondary (which he determines according to the longest spark). In the secondary he connects "additional coil" to the open secondary terminal. He checks the operation with harmonics so that he doubles the primary capacitance*, and by small regulations of primary inductance he changes the primary operating frequency, in order to achieve maximum effect on the secondary which is supposed to oscillate at double frequency - primary harmonic. He doesn't obtain the expected results and continues the experiment with capacitive loading changes in secondary circuit, and looks for most suitable elements in the primary circuit. He considers that he obtained the best result when sparks in the secondary are most powerful.
In continuation of experiments with the transmitter, he looks for an explanation for the appearance of largest current streamers in the secondary when the inductance of regulating coil in the primary circuit is reduced to a minimum (and then it is practically disconnected from the circuit). Tesla was confused with the fact that maximum voltage at the open end of the additional coil (this coil is connected to the secondary similar as on Fig. 2 on July 11) doesn't occur when the excitation current frequency is equal to the coil's self resonant frequency. After an extensive analysis, Tesla came to the correct conclusion (opposite to the one of June 30 which was correct only in a special case) that in cases where the secondary free vibration is emphasized, parameters, of the primary circuit have to be weighed such as to achieve the maximum voltage in the secondary, and the additional coil self-resonant frequency has to be equal to the frequency of the combined system primary-secondary. It appears Tesla did not assume that when the link is good, the combined system produces a distinguished spectrum during and after spark interruption. It seems to us that much more important is the abovementioned conclusion which he established when combining the experimental results, simple theory and intuition.
When experimenting with his oscillator, Tesla observed that during a discharge in the secondary the sparking appears on lighting arresters as well. As these arresters are connected to the supply feeder, he assumed that the high frequency voltage originates from a wave which propagated through the ground, and at a certain location entered the feeder. The data is missing which would help to establish whether this high frequency voltage is actually a consequence of the oscillator link via supply transformer with the supply feeder.
In third part of notes on July 24 he gives measurement results of secondary coil capacitance as a whole with respect to the ground. He didn't mentioned how he performed the measurement by comparison with standard capacitor and then, by using several methods he calculates the wire capacitance of the same length as coil wire (C1) according to the equation for capacitance of a single ellipsoide of which the longer axis is considerably longer than short one, and C2 according to the equation for conductor capacitance above an ideally conductive plane under the condition when the distance from the plane is considerably larger than wire radius). Expanding on considerations for capacitances, he describes the methods for achieving the largest capacitances, and moves further and further away from his initial topic. He ends the notes with a discussion on the spheres filled with hydrogen which were supposed to have maximum capacitance for given dimensions, and which would therefore be used for telegraphy without wires.
* In order to get the primary to oscillate on two times lower frequency, the capacitance has to be four-fold. It is possible instead of series connection 8-9 jars which is equivalent to 4-4 1/2 jars he connected two previous series connections in parallel, and obtained the equivalent capacitance of 16-18 jars, that is four times larger than the equivalent capacitance of jars connected in series.
