Nikola Tesla Books
Books written by or about Nikola Tesla
| Coil on drum | 26" diam. | ||||
| upright stand | No. 6 wire | 136 turns | |||
| Coil on spool | 12" diam. | 2 1/8" long | 28 layers Bell wire No. 18 | ||
| turns | { | to 20 lay. 28 | } | = 20 x 28 + 8 x 27 = 560 + 216 = 776 turns | |
| " 28 lay. 27 | |||||
* Exp. to determine periods of vibration.
New extra coil as first wound 8' 3" diam., 8 ft. long, 105 turns No. 6 wire, between grooves 1/2". A number of these coils have been before described and their inductances measured. Since the same drums were repeatedly wound with different wires it is easy to determine the inductances on the bases of data before recorded with some of them. It is proposed to make later a complete table of the coils with the inductances and other particulars worked out.
Colorado Springs
Dec. 16, 1899
In carrying on some experiments to ascertain the effects of induction from the primary circuit of the oscillator in the laboratory, at a distance from the same, a square frame described on a previous occasion was used. This frame was 11' 1/4" = 132.5" = 336.55 cm long and as much wide and 3 3/4" = 9.525 cm deep. It was wound with 14 turns of wire No. 10. To ascertain the period of vibration of this coil a formula before arrived at and frequently used was again employed. This formula applies to coils of circular cross section but it was thought that the results would be close enough also for the square coil with due allowances. To apply the rule the square surface was converted into a circular one equal to it and the diameter of the latter was calculated. Finally an allowance was made for the diminished length of the wire on the circular coil for the same number of turns. Calling D the diameter of the circle we have $! {D^{2} \pi \over 4} $! = 336.552 from which follows D = 380 cm. approximately. The formula referred to is
p = $! {{3 \times 10^{10} \sqrt{(Ï + d)Ï}} \over {D^{2} N \sqrt{Ï^{3} K} \sqrt{d}}} $!
Here Ï=distance of wires=0.46 cm; d=diam. of wire=0.254 cm;
(Ï + d) = 0.714; $! {\sqrt{Ï (Ï + d)}} $! = 0.573;
K as found = $! {52 \over 10^{6}} $!; $! {\sqrt{s}} $! = 0.5; N = number of turns = 14; p = natural frequency of coil to be found.
This gives in the present case:
p = $! {{3 \times 10^{10} \times 0.573} \over {3.1416 \times 380^{2} \times 14 \times \sqrt{{3.1416 \times 52} \over 10^{6}} \times 0.5}} $! =
320
December 16
Tesla applies one previously developed equation for the determination of coil selfresonant frequency of the square frame (please see notes on July 11, 1899). As the equation was developed for a circular coil he performs the correction of obtained results for the square coil*. The correction is in multiplication of the obtained resonant frequency with a ratio of wire length in coils of rectangular and circular cross-section.
At the end of the same day there is a note that the experimental result is approximately matched with the theoretical one but there is no description of the experiment.
During the period of Dec. 17 to 31, Tesla produced 14 photographs together with a photograph of Mr. Alley (this is the only complete name mentioned in his notes) which he sent from him to his friends, probably to associates of the magazine "The Century Magazine".**
In the archives of the Nikola Tesla Museum in Belgrade a certain number of original negative plates were found (approximately half of a total of 63 photographs which are mentioned in the notes) and some of the contact-copies. Several so far not published, identified, photographs are attached to Tesla's description of the photographs. The photographs were copies and published (total of 12 of them in articles(1, 41) for the purpose of completion. Except in one case when it was not established for certain which photograph of four described corresponds to the found ones, all photographs are designated by Roman numbers as in Tesla's notes.
Viewed as a whole the photographs impress with their composition, content and technique. Undoubtedly photographer Mr. Alley and Tesla himself contributed to this effect. There are unusual photographs taken with moonlight and the photographs of the inside of the laboratory made with the light of electrical discharge. Also the photo transpositions were made with a flashlight to see the devices' contours (and somewhere the human figure would be in there for the purpose of reconciling the dimensions), and then the artificial lightning was photographed. The electrical discharge at the oscillator secondary terminals or various coils was photographed with several devices being switched "on" and "off" during the photographing of one such event.
By means of this method many photographs were made with rich current streamers and sparks, which makes these photographs nicer, but less realistic. Sometimes one hundred device "on" and "off" switchings were performed in order to get one photograph. Because the description of numerous photographs is such that further comments are not necessary, we will only pay more attention to some photographs where it is necessary to pinpoint facts or data which will contribute to easier reader orientation.
* With "circular" and "square" the coil core cross-section shape is indicated.
** This magazine in June l900 published Tesla's known article under the title "The Problem of Human Energy Increase"(41). In this article several photographs of Tesla's laboratory in Colorado Springs were shown (total of nine). Experiments with the big oscillators are mentioned as well, but the manner of writing is quite different from the notes. While for example, in the notes the apparatus details are precisely described and its operation is commented upon, in the mentioned article the events and experiments are taken as the proof of certain of Tesla's hypothesis.
