Nikola Tesla Books
Books written by or about Nikola Tesla
into the air. The longest were only about 4 feet as it was deemed unsafe to strain the apparatus higher until further provisions for safe working were made. The lightning arresters were observed but no sparking. This showed that the absence of sparks was not due to rain or moisture as was concluded yesterday, since the weather was very warm and dry.
Colorado Springs
Aug. 30, 1899
Experiments were resumed with resonating coil to be used in connection with receiving apparatus. The coil was wound a week before on a drum 25 1/4" diam. of bicycle hoops and a thin board, the idea carried out before in New York being followed to make the drum with coil serve, at the same time, as a table for instruments. The drum was 3 1/2 feet high, only partially wound on upper part. The wire was ordinary magnet wire No. 20, 516 turns. The self-induction was approximately calculated from the following data: diameter of dram 25 1/4" or 64 cm.; length of wound part 20" or 50.8 cm.
$! {L = {{4 \pi \over 10} \times {{\pi \over 4} \times {d^{2} n^{2} \over 1}}} = {d^{2} n^{2} \over 1} = {{64^{2} \times 516^{2}} \over 50.8} = 0.02} $! henry approx.
Taking n approximately 50,000 per second it was close enough for the purpose to assume p = 300,000.
The resistance of wire being 34 ohms we had
$! {{Lp \over R} = {{300,000 \times 2} \over 3400} = 177} $! fairly good.
The coil was now tuned with oscillator in response to a somewhat higher note with small capacity on free terminal, the other being connected to the water pipe. Sparks of 3/4" were obtained while from the water pipe alone a very minute spark, scarcely perceptible, could be obtained. Induction from primary being carefully eliminated, the sparks were still 3/8" long and white.
Colorado Springs
Aug. 31, 1899
Experiments were continued with the extra coil and secondary conditions as before. The ball in the center was connected again to the top of coil and elevated a little above the roof, the latter being opened as wide as possible. The experiments were begun in the afternoon while the Sun was very bright. Scarcely any streamers from the ball could be seen but occasionally sparks would go to the roof from the center wire leading to the ball. The distance was 12 feet. There was a pronounced tendency in the sparks to fly to the roof which might have been due to dampness of the latter owing to rain the day before. During
167
August 29
Although the circuit looks simple enough, an analysis of Teslaâs receiver with a âmagnifying effectâ is rather complicated, because transient phenomena have to be taken into account and the resistance law of the sensitive devices as a function of voltage has to be known. It was not easy to adjust a receiver like this to work properly.
Apparently there was an earphone T in the secondary circuit of the transformer, but it is not mentioned in the notes. The sensitivity of an earphone would normally be much greater than that of a relay, so it would be interesting to find out how this apparatus performed. Unfortunately, earphones are practically not mentioned anywhere in the diary.
Tesla here at last makes a few remarks about how the sensitivity of receivers was estimated. To test its response he put a âsmall capacityâ across sensitive device a, but of what value, and whether it was charged or not he does not say.
August 29
He describes the receiver with the oscillator and two sensitive devices. This time, instead of a rotating breaker, driven by a clock mechanism, he uses a fast mercury rotating breaker; and instead of circuit elements of the standard receivers, he takes the transmitter circuit. The oscillator transformer serves as excitation amplifier. Tesla's idea of a receiver with an "amplifying effect" could be easily understood by this example. Sensitive device 'a', changes the excitation of oscillator with mercury breaker. This excitation causes the rise of high frequency voltage in the secondary for the higher absolute amount (due to voltage transformation) and therefore the sensitive device 'a1' is more excited than the device 'a' was. Although the circuit appears very simple, the analysis of such a receiver is quite complicated because it is necessary to consider the transient events and to know the losses dictating the changes in sensitive device resistance with supply voltages. It was not easy to adjust such a receiver in order to get it operating correctly.
Tesla put the earphone T in the secondary circuit of the transformer, but in the text he doesn't say anything about it. The earphone sensitivity is normally much higher than the relay sensitivity and therefore it would be interesting to know something about Tesla's experience with this device. Unfortunately, there is no mention in his notes about an earphone.
Finally, Tesla said a little bit about the receiver's sensitivity measurement. In order to check the devices reaction, he puts a small capacitor in parallel with sensitive device 'a'. How big that capacitor is, whether charged or not, he did not say.
August 30
He experiments with the "resonant coil" which he intends to use for the receiver. The coil requires the capacitance of 506 picofarads in order to achieve resonance at 50 KHz. With a small capacitance, which it appears Tesla added, the spark about which he talks could have been due to a harmonic oscillator frequency.
August 31
Again he works with the oscillator, "additional coil" and capacitive loading in an old layout. The aerial with the sphere was going through the opening of the roof of the laboratory (refer to laboratory photographs). Due to the humidity he performed short tests. In a few cases he checked the lightning protector, but there were no sparks on it. The test of the supply line indicated that one supply line has a good connection with ground. It is assumed that he finally found the cause of the nonexistence of sparks on the lightning protector.
During the experiments he observed that small insects are killed when they are within the strong electro-magnetic field of the oscillator.
When current streamers are non-existent, the tendency of capacitor flashover in the primary circuit appeared. The explanation is simple: the current lines represent the secondary load and when they don't exist, voltages in both oscillator circuits rise.
