Research of Nikola Tesla in Long Island Laboratory
After completing grandiose research in Colorado Springs Nikola Tesla returned to New York and started to look for money and the place where to build a new laboratory. This time he wanted to make a commercial plant--the "World System" power plant--as he called it. About the time he returned to New York Tesla wrote a long article in the Century magazine about his experiments in Colorado Springs. The editor of the magazine tried to persuade Tesla to write a more understandable paper, but his efforts were not very successful. In the end Tesla wrote something that looked more like an essay rather than a typical scientific paper. The length of the paper was also unusual--it was as long as his lectures that he delivered earlier before various scientific gatherings. After "Colorado Springs Notes 1899-1900" were published in 1978, a new material was put forward to researchers, and many queries from the Century article became clarified. However, a veil of unknown remained, especially in connection with Tesla's later research in Long Island Laboratory. For a long time we have studied Tesla's notes which he wrote in the period 1900-1906 and in this paper we want to present some of the findings that will help to understand Tesla's research in this period.
2. LONG ISLAND NOTES IN NIKOLA TESLA MUSEUM
In contrast to Colorado Springs Notes that were neatly assembled by Nikola Tesla himself, Long Island Notes were scattered through his scientific papers. It will be some time before all Notes are collected together, but it is clear that there will be no great change as to the amount of dated notes in comparison to what we have already found.
Some Long Island Notes are written by pencil, some by ink. The sizes of notes vary considerably. Sometimes there are only few lines or few formulae, or some calculations. Less than one third of the notes are neatly finished similar to the Colorado Springs Notes.
In 1900 Tesla's notes contain only 8 leaves. That number increases to 141 in 1901, 196 in 1902, 272 in 1903, drops rapidly in 1904 to 13 only, there are no notes in 1905 and then there is a jump to 50 leaves in January 1906, only. With the title "Notes to Long Island Plant," written by Tesla on the folder we found 73 leaves without dates. On the following pages we have given a Table showing the number of leaves written on the specified dates. Later we will discuss the content of the Notes.
The Notes in 1901 are written by ink (except few that are written by pencil) in a similar fashion to the Colorado Springs Notes. The handwriting can be read without much difficulty, typical page being like the one shown (May 19, 1901 ). The rest of the notes are written by pencil. Some of the notes are difficult to read, especially those written later.
LONG ISLAND NOTES
3. SUMMARY OF RESEARCH TOPICS IN DATED NOTES 1900-1906
Dated notes, as explained in chapter 2, contained over 600 leaves and it is not an easy task to cover even main topics created in the Notes. It should not be expected that all important thoughts or results (experimental or theoretical) will be given. We have read most of the material trying to discover interesting topics in the Notes. However, Tesla's handwriting is not easy to read and further efforts are needed to "decode" all the Notes and make them prepared for detailed study.
3.1. Notes written in 1900
As mentioned earlier there are only 8 leaves as the record of four days of work. At the very beginning of 1900 Tesla was in Colorado Springs for at least a week (last date in the Colorado Springs Notes was January 7, 1900). First notes written in the Colorado Springs Notes were dated June 2, 1900 and refer to insulating conductors by freezing. In late November, 1900, there were four pages that deal with new plant problems.
3.2. Notes written in 1901
In 1901 Tesla began to look for "approximate theoretical estimate of constants determining wavelength of electrical disturbance through Earth." The capacitance of the Earth he calculated as the capacitance of a metal sphere of the globe size. Then he calculated the radius of an equivalent cylindrical conductor, r, which have the same capacitance as the considered sphere. From the equality of the sphere capacitance and the capacitance of equivalent cylindrical conductor of length 0 (Tesla neglected the edge effects), he obtained r and C from the equation:
To calculate inductance of the Earth Tesla assumed that it is equal to the inductance of the equivalent cylindrical conductor, L:
where for the equivalent conductor he calculated inductance ignoring "magnetic influence." For the Earth diameter he assumed to be 7914 miles so that,
--total capacitance of the cylinder 707.5 uF = C = c·D
From the above values capacitance per mile and inductance per mile were calculated (the length of conductor was assumed to be 7914 miles, the Earth diameter). From the calculated c and 1, Tesla obtained the relationship between frequency and the wavelength along the cylindrical conductor (Long Island Notes, January 29, 1901):
The idea behind this relationship is based on the following statement from the insert of February 2, 1901 notes (citation):
Developing Long Island plant Tesla considered mainly the transmitting tower, oscillators for production of HF currents, choice of operating frequency, design of various coils, arrangements of terminals, etc. His propagation theory was based on the charge redistribution along the globe. As he did not consider only the static case, for higher frequencies (in this case frequencies above few Hz) he assumed that the zones of a half wavelength extent contain alternatively positive and negative electric charge. He considered transmitter frequencies as low as 4 Hz, but he devoted more attention to 60 Hz. On June 8, 1901, he wrote:
C·p2 = 150 746, from which . . . P = 409700 V . . ."
Continuing further his consideration along these lines, Tesla came around with figures that with 100,000 cm capacity terminal on the polar cap (a point on the opposite side of the globe to the transmitter location), one could get about 2 HP, which, in his opinion ". . . is enough to demonstrate practicability of power transmission."
An interesting summary appeared on October 13, 1901 (citation):
3.3. Notes written in 1902
The Notes are scattered throughout the year but there are two peaks--one smaller in March--and the other in October-November. In March period he dealt with experimental matters: he measured some coils, capacitances and frequency of laboratory oscillators. In October, a number of new considerations regarding his theory of current propagation through the Earth appeared. On October 8, 1902, he wrote in his notes:
For Tesla the Earth was nothing else but a metal ball, so it is natural that he tried to verify his theory of current propagation through the Earth by measurements on a metal ball. In October, 1902, he proposed a number of experiments to test his theory. The idea was to make a cage in the form of a sphere and pass very high frequency current through such structure (taking product of sphere diameter and operating frequency the same in the two cases). He expected to find that the wavelength change along the sphere cage, (imagining it as a conductor of variable cross-section) indicating that the velocity of propagation is constant along the axis of the sphere. Experimentally he tried to measure inductance of the sphere by replacing it with a straight conductor which inductance could be calculated. He also wanted to measure capacitance of "zones"--spherical rings. In a substitution sphere-straight conductor, in one measurement on November 3, 1902, Tesla found that "the induction of sphere 38.1 cm radius would be 45 cm. . ."
In November Tesla measured extensively various capacitances using balanced bridges. Occasionally he would return again to his theory of current propagation.
3.4. Notes written in 1903
For about half a year in 1903 Tesla wrote many pages of his Notes. Between January and May he performed many measurements of ground resistance and insulation resistance of the tower. He was careful ground resistance as can be seen from numerous calculations of power losses due to this resistance, and heavy current he wanted to use. The currents he considered varied between 2000-3000 A and obviously even 1 ohm of ground resistance would cause a great loss. He even calculated temperature rise caused by ground losses. He considered grounding by the use of a large metal sphere, metal pipes, and spreading of salty water around the grounding. Another important aspect of losses was in connection with the tower leakage. Tesla measured resistance between tower and grounding in various weather conditions, and in various times of the day and night.
In May, 1903, Tesla again turned more intensively to his theory of propagation. This time, and this is rather rare in all Tesla's notes, he refers to names. On May 21, 1903, he wrote:
On May 24, 1903 he began his discussion on radiation from the Earth by quoting a formula from Maxwell's book for the radiation of sphere charged to a potential P. Later he tried to make use of the same principle in calculation of radiated power by non-uniformly charged sphere.
3.5. Notes written between 1904-1906
There are few notes written in this period. They refer again to some earlier considered matters: oscillator design, maximum performance of electrical machinery (1904), some aspects of his theory (1906).
4. DISCUSSIONS AND CONCLUSIONS
The ideas which were developed, and the results of research which Tesla carried after his return from Colorado Springs in January 1900 were not fully disclosed in Tesla's papers which he published after 1900. Something was disclosed in  in 1904. Here Tesla explained his intelligence transmission "World Telegraphy" plant at Long Island. However, very little is said about technical details, most of statements .are prediction-like types. From technical point of view, more interesting things had been disclosed in 1912 paper . Another description of Tesla's system is found in a handbook . Tesla's claim that "his" system is different from "Hertz's" is based on the fact that at low frequencies, and with small antenna I in terms of wavelength, radiation of Hertzian type electromagnetic wave is small. "Tesla's waves," if we are allowed to use such a name, are in fact surface waves in modern terminology (as known, this type of waves are significant in the range of long waves) or the Earth cavity waves, known better as ELF (extremely low frequency) waves. In "pure Hertzian" wave (in Tesla's terminology) there is no induced current in the Earth, except on reflection region which is not essential for the discussion. In contrast to the latter, guided surface or ELF waves do not exist without current in the Earth crust. Having this in mind, we can conclude that there is a truth in Tesla's statements about specific behavior of low frequency, guided to the Earth waves. As regards correctness of his approach to the propagation theory based on outlined assumptions, more study is needed and we hope that it will be done in the future.