Various Tesla book cover images

Nikola Tesla Books

Books written by or about Nikola Tesla

Nikola Tesla: Colorado Springs Notes, 1899-1900 Page 321

December 16-31, 1899

= $! {{6 \times 10^{10} \times 573} \over {3.1416 \times 144,400 \times 14 \times \sqrt{3.1416 \times 52}}} $! = $! {{6 \times 10^{8} \times 573} \over {44 \times 1444 \times \sqrt{3.1416 \times 52}}} $! =

= $! {{3438 \times 10^{8}} \over {44 \times 144 \times 12.8}} $! = $! {{3438 \times 10^{8}} \over {813,300}} $! = $! {{3438 \times 10^{6}} \over 8133} $! = 423,000 approximately

and n = $! {423,000 \over 2 \pi} $! = 67,360 nearly.

This would be for a cylindrical coil of 14 turns, but the turns of the square coil are longer and, since the inductance is proportionate to the square of the length of wire, and the frequency again proportionate to the square root of the inductance, n will be smaller in proportion $! {{4 \times 336.55} \over {3.1416 \times 380}} $! = $! {1193 \over 1346} $! or the system will vibrate about $! {1193 \over 1346} $! x 67,360 or roughly 60,000 per sec. The experiments showed it vibrated nearly this number of times.

Colorado Springs

Dec. 31, 1899

Of the photographs taken here from Dec. 17 to Dec. 31, 1899 by Mr. Alley the following were forwarded through him to my friends of the Century:

I. Front view of laboratory from Pike's Peak side. Isochromatic 11' x 14" plate. Time - afternoon before sunset. This is a very fine photograph showing well the advantage of the pure atmosphere here. Such sharpness of outlines and amount of detail could not be obtained in New York, for instance. I conclude that the high quality of photographs obtainable in these parts is not so much due to the skill of the professionals as to the pure atmosphere and abundance of light.

II. View of interior showing half of circle of oscillator frame with several coils grouped inside; Westinghouse transformer, lightning arresters in background, also part of central “extra coil” latest pattern and a 30“ ball on stand. The photograph was taken late in the afternoon. Light was rather feebly diffused. The plate was as before, 11" x 14" isochromatic.

III. View of interior, chiefly showing condensers, break motor and regulating coil in primary of oscillator. Westinghouse high tension transformer and supply transformers in background, also arresters. Plate same as before, the photograph was taken at the same time, practically as that described under II. The diffused daylight was very feeble. Both of these plates are excellent.

IV. View of laboratory from the rear by moonlight; 1 h 20 min. exposure. Moon about 2/3 full. Showing Pike's Peak Range and all details of building very sharply. Such photographs by moonlight could be secured only in a few places. Plate same as before, 11" x 14" isochromatic.




Wait, J.R. “Historical background and introduction to the special issue on extremely low frequency (ELF) propagation”, IEEE Trans. on Communications, Vol. COM-22, No. 4, April 1974.

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.


Lowercase tau - an irrational constant defined as the ratio of the circumference of a circle to its radius, equal to the radian measure of a full turn; approximately 6.283185307 (equal to 2π, or twice the value of π).
A natural rubber material obtained from Palaquium trees, native to South-east Asia. Gutta-percha made possible practical submarine telegraph cables because it was both waterproof and resistant to seawater as well as being thermoplastic. Gutta-percha's use as an electrical insulator was first suggested by Michael Faraday.
The Habirshaw Electric Cable Company, founded in 1886 by William M. Habirshaw in New York City, New York.
The Brown & Sharpe (B & S) Gauge, also known as the American Wire Gauge (AWG), is the American standard for making/ordering metal sheet and wire sizes.
A traditional general-purpose dry cell battery. Invented by the French engineer Georges Leclanché in 1866.
Refers to Manitou Springs, a small town just six miles west of Colorado Springs, and during Tesla's time there, producer of world-renown bottled water from its natural springs.
A French mineral water bottler.
Lowercase delta letter - used to denote: A change in the value of a variable in calculus. A functional derivative in functional calculus. An auxiliary function in calculus, used to rigorously define the limit or continuity of a given function.
America's oldest existing independent manufacturer of wire and cable, founded in 1878.
Lowercase lambda letter which, in physics and engineering, normally represents wavelength.
The lowercase omega letter, which represents angular velocity in physics.