Various Tesla book cover images

Nikola Tesla Books

Books written by or about Nikola Tesla

the rarefied gas in the bulb and there is a corresponding diminution of the effective resistance of the lamp on this account. In fact, I think that it is chiefly owing to this that the resistance becomes very small, it being a fact that such currents pass with the greatest freedom through the rarefied gas particularly when it is maintained at a high temperature, as in the case here considered. The heating of the gas has the effect of increasing the incandescence of the carbon and it is well demonstrated that an incandescent lamp takes, for a given luminosity, less energy when operated with currents of such extreme frequencies. Owing to these reasons the magnifying factor of the excited system even with the lamps included must have been very much larger than the figure last mentioned. It was astonishing to note, in the experiment recorded on the plate, how much energy can be in this manner conveyed to such a carefully synchronized coil through the ground. The supply transformers were cut down by a regulating coil in the primary to less than one half, in fact to about 1/3 of full capacity and inasmuch as only 3 tanks on each side in the primary or exciting circuit were used while 8 tanks were available, it is evident that, if the excited system would have been designed to work with full output of the exciting apparatus it would have been quite practicable to light, say 3 x 8/3 = 8 times as many lamps, or about 40 lamps. However, inasmuch as the five lamps were far above candle power it would have been, in all probability, possible to light 60 lamps or so to normal candle power by a specially designed coil, with a liberal allowance of copper, vibrating in unison with the system exciting the portion of the ground containing the ground plate. Nothing could convey a better idea of the tremendous activity of this apparatus and a simple comparison with well ascertained data, obtained with other induction apparatus, shows that one of the problems followed up here, that is the establishment of communication with any point of the globe irrespective of distance, is very near its practical solution. The existence of stationary waves proves the feasibility of the project almost beyond any doubt. The great amount of energy which can be conveyed to such a synchronized circuit, by conduction through the ground, makes it appear possible, that the necessity of elevating terminals in my system of energy transmission to a distance may be dispensed with in many instances and that, with a very moderate elevation of, say, a few hundred feet enough energy may be conveyed to a circuit to serve for one or another useful purpose beyond mere signalling, or such uses of the system in which a minute amount of energy is required. Certainly, the amount of energy conveyed in this manner was, in some experiments with this apparatus, surprising at first. An interesting consideration in this connection may be the following: As before stated the period of the exciting or primary circuit, when resonance with the extra coil was attained, was Tp = $! {{2 \pi \over 10^{3}} \sqrt{0.0486 \times {6 \over 10^{5}}}} $!. Now the period of the excited system was Ts = $! {{2 \pi \over 10^{3}} \sqrt{0.018 \times C_{s}}} $!, in which Cs is the “ideal” capacity as designated in previous instances, that is the capacity which would have to be joined to the free end of the “extra coil” of inductance of 0.018 henry but devoid of all distributed capacity. Since Tp = Ts we find Cs = $! {{0.0486 \times {6 \over 10^{5}}} \over 0.018} $! mfd, or

Cs = $! {{9 \times 10^{5} \times 0.0486 \times {6 \over 10^{5}}} \over 0.018} $! = $! {{54 \times 0.0486} \over 0.018} $! = $! {{54 \times 486} \over 180} $! = $! {{3 \times 486} \over 10} $! = 145.8 cm.


The explanation to Photograph XXII concerning the transmission of power from the excited primary circuit to the “extra coil” via the earth is similar to that he gave in 1893(6). The experiment to which the photograph refers was made with the aim of estimating the power of the oscillator from the thermal effect of the HF current. What Tesla calls the “total energy set in movement” would correspond to the total energy transferred to condenser in the secondary (i.e. the power) if an energy of $!{1 \over 2}$! CV2 is transferred in each half-cycle. It can be shown that the active power dissipated in the circuit is much less than this and is inversely proportional to the Q-factor of the oscillating circuit.

January 2

Tesla gave his observations on 22 pages. On them he described eleven photographs. The explanation along with photograph No. 22 about energy transmission from excitation of the primary circuit to "additional coil" over the earth surface is similar to the one from 1893(6). Otherwise the experiment to which the photograph is related was performed for the purpose of oscillator power estimate on the basis of thermal effects of high frequency current.

That which Tesla calls "total energy placed in motion" would correspond to the total energy which is supplied to a capacitor per second (i.e. power) if energy ½CV2 is supplied during the duration of one half of the period. 

It could be shown that the active power which is spent in the circuit is considerably smaller than this power, and opposite, proportionally to the quality factor of the oscillating circuit. On several following photographs, the movable resonant coil with connected bulbs is photographed which is supplied by transmitted high frequency energy. One terminal of this coil is connected to the ground, and the other is open ended or a short piece of wire is connected to it. Bulbs are coupled by means of the auxiliary secondary coil inductively with the secondary coil. The data was not given on the distance of resonant coil from the oscillator coil. Tesla's comment on photograph No. 27 illustrates the interest on the question of electrical lightning, though he worked on this for more than ten years. One earlier discovery on gas elimination and not only filament, when working with high frequency currents is again proven(5).

On photograph No. 28 the bulb is connected in series with a terminal capacitance load. In the calculations "total energy placed in movement" is not taken when it was assumed that the electrostatic energy ½CV2 is spent in the bulb during one half of the period. A similar comment is valid for photograph No. 29.

Tesla mentioned several times that the main transmission from the exciting to the excited circuit is done via the ground. The proof for this statement he found in the experiment illustrated by photograph No. 30. He concluded that the induced voltage in the excited circuit is significantly reduced when the ground connection is disconnected. Photograph No. 31 is an X-ray photograph of a finger. The comments on this experiment are an illustration of Tesla's interest in the radiation field which was mentioned earlier (please see comment on June 6, 1899).


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.