Nikola Tesla: Colorado Springs Notes, 1899-1900 Page 365

January 2

In this entry of 21 pages (the longest in the Notes) Tesla describes 11 photographs.

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.

The next few photographs show a movable coil which powers light bulbs by means of the high-frequency power which it picks up. One end of the coil is grounded, the other free or just connected to a short piece of wire. The bulbs are inductively coupled to the resonant coil via the auxiliary secondary. Tesla gives no data about the distance of the resonant coil from the oscillator coil.

Tesla's commentary on photograph XXVIII illustrates that he still retained a lively interest in the problem of electric lighting, even after a period of over ten years. His earlier discovery of the luminescence of the gas and not only the filament with HF currents was here again confirmed⁽⁵⁾.

In photograph XXVIII the bulb is connected in series with the terminal capacitive load. In the calculation Tesla does not use the “total energy set in movement” but assumes that 1/2 CV² of electrostatic energy is consumed in the bulb in each half-cycle. A similar comment applies to photograph XXIV.

Several times Tesla remarks that the principle energy transfer from the oscillating to the receiving coil takes place via the earth. He finds confirmation for this in the experiment described on p. 363 (photograph XXX). He found that the voltage induced in the receiving coil was greatly reduced if the ground connection was broken. It may be that such experiments led him to the conclusion that “transmission” through the earth was a more efficient method of wireless transmission of power than the “inductive method”.

Photograph XXXI is an X-ray picture of a finger. Tesla's comments on this experiment illustrate his interest in this type of radiation, already referred to (see the commentary to 6 June 1899).

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).

January 3

After describing some photographs of the laboratory, in the commentary to photograph XLI Tesla explains some transformations of the streamers. He mentions the splitting of streamers near the floor, splitting and reuniting, the phenomenon of luminous parts on the streamers (which he then refers to as sparks), and the breaking up of sparks into streamers and fireballs. His remarks concerning the genesis of fireballs are particularly noteworthy. This phenomenon has been a source of interest since ancient times. Some references to it can be found on Etrurian monuments, in the works of Aristotle, Lucretius and other old sources⁽⁶³⁾. Fireballs are considered to be a form of electrical discharge generated during thunderstorms. They are rare in nature, but a fair-sized body of observations has nevertheless been assembled upon which several theories of their origin have been founded. Some hypotheses maintain that fireballs are an optical illusion (an opinion shared by Tesla until he produced them himself), others that they are the traces of meteors. The first genuine scientific approach to the problem was Arago's analysis of some twenty reports of fireballs in 1838. After the publication of his work they became a legitimate subject of scientific interest, but to this day have remained something of an enigma.

A fireball is a luminous sphere occurring during a thunderstorm. Fireballs are usually red, but other colors have also been observed: yellow, green, white and blue. Their dimensions vary, a mean diameter being about 25 cm. Unlike ordinary lightning, fireballs move slowly, almost parallel to the ground. They sometimes stop and change their direction of motion. They can last for up to 5 seconds. Their properties vary greatly from case to case, so that it is believed that there are various types. According to Singer⁽⁶³⁾ it can be stated that as yet no single theory can explain the occurrence of fireballs in nature.

Despite numerous attempts, only a few types of fireball have been created, and not entirely successfully, in the laboratory. These include the weakly luminescent fireballs generated when ordinary lightning strikes some object. Tesla mentions phenomena of this type several times as the result of sparks or streamers striking wooden objects (see e.g. photograph XL). According to recent theories, fireballs consist of a plasma zone created by electrical discharge. The latest research and calculations by Kapitsa⁽⁶⁴⁾ show that the lifetime of a fireball cannot be explained by the energy it receives at the time of genesis, but that it must receive energy from its surroundings. Kapitsa theorizes that this external energy is produced by a naturally created electromagnetic field. The small zone of ionized gas created by the initial lightning or other electrical phenomenon during the storm subsequently expands at the expense of the external electromagnetic field. The diameter of the plasma sphere is determined by the frequency of the external field, so that a resonance occurs. The usual dimensions of fireballs would require that the electromagnetic field have a wavelength of between 35 and 100 cm. According to this theory standing waves created by the reflection of natural electromagnetic waves from the earth would play a certain role. The theory has obtained partial experimental confirmation, but there are still many points on which it is unable to give a satisfactory explanation. It has been found that to maintain a lump of plasma in air requires a power of the electromagnetic field of about 500 W, which is much less than power which can be produced by an electrical discharge. However, too little is known about natural electromagnetic waves to allow any reliable conclusions to be drawn.

Tesla's hypothesis on the origin and maintenance of fireballs includes some points which are also to be found in the most recent theories, but it also bears the stamp of the time. For instance, like Kapitsa, Tesla considers that the initial energy of the nucleus is not sufficient to maintain the fireball, but that there must be an external source of energy. According to Tesla this energy comes from other lightnings passing through the nucleus, and the concentration of energy occurs because of the resistance of the nucleus, i.e. the greater energy-absorbing capacity of the rarefied gas than the surrounding gas through which the discharge passes. In nature the probability of other discharges passing through the nucleus of a fireball is small, so Kapitsa's hypothesis that act via electromagnetic standing waves is more logical. It is possible that in Tesla's experiments the “passage” of a number of later discharges through the same nucleus was more frequent.

January 3

After description of several photographs showing the laboratory on photograph No. 41, he explains some current streamer transformation. He mentions the current streamer division in the vicinity of the floor, the division and repeated merging of the current streamers, the event of brighter current streamer portions (which he calls sparks), and the distraction of the spark into current streamers and "fire-balls". Particularly interesting are Tesla's observations and comment about the creation of "fire-balls", the event which interested people for a long time. Some data about "ball type" lightning have been found even on Etrurian monuments, in the works of Aristotle, Lucretia and others⁽⁶³⁾.

Ball-like lightning or "fire-balls", as Tesla calls them, are created during weather disturbances and are considered one kind of electrical discharge. The event in nature is very rare, but nevertheless quite a bit of information has been collected on the basis of which several theories have been established on the cause of this lightning. According to some hypothesis, the "ball-type" lightning is an optical illusion (Tesla thought so as well until he produced ''fire-balls''), according to others this is the track of meteors.

Before Arag's analysis of approximately twenty known events of ball-type lightning in 1838, there was no scientific analysis in the real sense. After publication of Arag's work, ball-type lightning entered in the circle of science problems and they remain to this day a partial puzzle.

Ball-type lightning is a bright sphere, which appears during the storm. In most cases it is red in color, but appears in other colors as well; yellow, green, white and blue. Dimensions are various and the mean diameter is approximately 25 cm. As distinct from usual lightning, ball-type lightning moves slowly, and travels parallel to the ground. They could stop and change their direction of movement, and last even to to five seconds. The characteristics of ball-type lightning changes from case to case, and therefore it is considered that there are various kinds of this type of lightning. According to Singer⁽⁶³⁾, it is considered today that one theory does not give the explanation for all types of ball lightning in nature.

Despite numerous efforts, only some types of ball-type lightning have been partially produced under laboratory conditions. Amongst those are poorly lit balls created after a strike of usual lightning against some solid matter. Tesla several times mentioned similar events caused by spark strike or current streamer against a wooden object (please see e.g., photograph No. 50). According to new theories, ball-type lightning is in fact the plasma area created in nature by means of electrical discharge. Latest research and calculations by Kapica⁽⁶⁴⁾, indicate that the light of ball-type lightning is impossible to explain by means of energy which it could contain at the instant of creation, thus for its maintenance external energy should be supplied. Kapica assumed that the external energy is obtained from naturally created electromagnetic fields. In the beginning a small area of ionized gas, created by previous lightning, or some other electrical event during the storn, is increased on account of the energy of an external electromagnetic field. The diameter of the plasma sphere determines the frequency of the external field, and so the resonance is achieved. The most frequent dimensions of fire-balls require electromagnetic fields of 35 to 100 cm wavelength. According to this theory, it is assumed that some role is played by standing waves created by a reflection of natural electromagnetic waves from the ground. This was partially proven by an experimental method, but there are still problems to which even this theory did not provide satisfactory answers. It has been established that for the maintenance of the plasma chunk in the air, the required electromagnetic field power is approximately 500 watts, which is considerably below the possible power present during an electrical discharge. However, there is very little known about natural electromagnetic waves, and therefore on the basis of this limited data, it is not possible to conclude much.

Tesla's hypothesis of the creation and sustaining of fire-balls contains some assumptions which can be found in the newest theories, but it carries the characteristics of the time in which it was established, so, for example, according to Tesla and Kapica, if the initial energy nucleus of the fire-ball is not sufficient for the ball-type lightning sustenance then it is necessary to supply external energy. Tesla exhausts the energy from other lightning which propagate through the nucleus space of the fireball, and the energy concentration he explains by nucleus resistance, or the higher capability of a rare gas in the nucleus to absorb energy from the other gases which pass through the discharge. In nature there is less likelihood of several lightning strikes passing through the nucleus of a ball-type lightning and therefore the Kapica assumption on the action of other lightning strikes by means of an electromagnetic field and standing waves which they create, is more logical. In Tesla's experiments it is possible that there frequently occurs a ''transfer'' of repeated lightning over the nucleus of ball-type lightning.