Various Tesla book cover images

Nikola Tesla Books

Books written by or about Nikola Tesla

about 50 times and after this, as usual, an exposure to arc light for the detail of the apparatus was made, the time being 10 minutes with a small opening.

In order to make these two experiments still more interesting they were performed outside with a smaller receiving coil and photographs were taken, which are numbered and of which Plate XXIV. shows a coil standing outside on a table to which a ground-wire leads, which is connected to one of the terminals of a small lamp, while the other terminal of the same is joined to the lower end of the coil. The upper end of the coil is free, a metal tube being connected to the same, as shown clearly in the picture. This tube is placed axially and serves to increase slightly the capacity of the excited system.

In another experiment, with the same coil illustrated in Plate XXV., the coil is placed on the ground away from the laboratory and the lower end is connected to the nearest ground, while the upper end or terminal is free. Three turns of wire are wound around the lower end of the coil and the ends of this wire are connected to a lamp socket with its lamp which is, as shown, lighted by the currents induced in the three turns of wire through the oscillations transmitted through the ground to the coil.

One more experiment of this kind was photographed, the same coil being again used and placed far out into the field, this being shown in Plate XXVI., giving a clear view of the Pike's Peak Mountain Range in the background. The diagrams and several remarks before made apply to some extent also to these three photographs which were taken after sunset when the dark began to set in, as it was impracticable to take them at another hour of the day. They might have been taken by moonlight but the time was otherwise occupied. During the hours when the light was strong it would have been necessary to exclude first the daylight in some way, flash the lamp in the dark and finally make a short exposure to the full daylight to get the detail of the apparatus. It was found impracticable to get a good photograph by flashing the lamp in full daylight as the latter was too strong and the lamp did not have enough time to impress the plate as strongly as was desirable, even if it was pushed to much higher candle power than the normal. In getting the photographs, generally about 100 throws of the switch were sufficient with the lamp being pushed considerably above the normal. When the daylight was still deemed too strong Mr. Alley helped himself by covering the lens during the short interval when the lamp was not lighted and thus regulated the effect of the daylight, keeping it down to the required value.

The particulars were as follows: The coil used in these three experiments was wound on a drum before referred to of 25.25" diam. and had 274 turns of wire No. 10, rubber covered. Since another coil wound on the same drum had 404 turns and an inductance of approximately 40,000,000 cm. or 0.04 henry the inductance of the present coil was with fair approximation $! {\left({274 \over 404}\right)^{2}} $! x 0.04 henry or $! {\left({137 \over 202}\right)^{2}} $! x 0.04 henry. The wire leading from the ground plate to the lower end of the coil placed on the table or ground consisted of two pieces of cord No. 10, one 308 feet and the other 84 feet long. The inductance of these two pieces of wire was estimated at 113,000 cm and compared with the inductance of the coil itself was very small, almost negligible. Calling the total inductance of the excited circuit comprising the two pieces of wire and the coil used L1 we have for this inductance value L1 = $! {\left({137 \over 202}\right)^{2}} $! x 40,000,000 + 113,000 = 18,400,000 + 113,000 = 18,513,000 cm, or L1 = $! {185 \over 10^{4}} $! henry. This inductance, with its distributed capacity, gave a system responding




Hertz, H.R. UNTERSUCHUNGEN UBER DIE AUSBREITUNG DER ELEKTRISCHEN KRAFT, dritte auflage, Leipzig, 1914, Johann Ambrosius Barth.

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.