Nikola Tesla: Colorado Springs Notes, 1899-1900 Page 30

June 6

Working with a darkened Crooke's tube, on the 8th of November 1895 Rӧntgen noted the luminescence of barium platino-cyanide crystals and discovered that it was due to some unknown radiation which he termed X-rays. Towards the end of that year he held a lecture on his discovery, and in an amazingly short time the whole world knew about his work⁽⁶⁶⁾.

Tesla spent some time in intensive research on X-rays, publishing his results in ten articles in the period 11th March 1896 to 11th August 1897⁽⁷⁾. On the 6th of April 1897 he also gave a lecture on his X-ray studies⁽¹⁷⁾ and presented designs of a number of devices for generating powerful rays. During this lecture he reported interesting data from his earlier experiments with Crooke's tubes in 1894. He had then observed that some tubes which produced only feeble visible light had more effect on photographic plates than tubes which were brighter to the eye. The goal of his research was to obtain true phosphorescence (“cold light”), so that he postponed further investigation of this phenomenon, and of the cause of various spots and hazing on photographic plates which had been kept in the laboratory for a time before use. When he finally did get around to it a fire broke out in the laboratory, destroying practically everything (13th March 1895). It was several months before he could resume his work, and in the meantime Rӧntgen made his discovery. When Tesla heard about it, it was immediately plain what had been happening in his laboratory. He repeated Rӧntgen's experiments, which were rather cryptically described, and realized that he had been mistaken in not following up certain chance observations during his work with Crooke's tubes.

During 1896 and 1897 Tesla carried out many experiments with X-rays, also speculating about their nature. He thought “that the effects on the sensitive plate are due to projected particles, or else to vibration far beyond any frequency which we are able to obtain by means of condenser discharges” (Lit.⁽¹⁾, p. A-30). He immediately realized the importance of high voltages for producing powerful rays and suggested using his single-terminal tubes connected to the secondary of the disruptive discharge coil. It is interesting to note that Rӧntgen too, in a lecture to the Physical Medical Society of Würzburg the same month as Tesla published his first article, also pointed out the great advantage of using Tesla's high-frequency oscillator in generating X-rays.⁽⁶⁶⁾

Tesla measured the reflection and transmission of X-rays for several metals, lead glass, mica and ebonite. It is not clear, however, whether what he measured was true reflected radiation or secondary radiation. He also tried to detect refraction but did not succeed, for reasons which are today obvious. In papers and in a lecture before the New York Academy of Science he described a number of tubes for producing powerful X-rays, most of them resembling Lenard tubes (which he often mentions) but without the anode terminal.

June 6

During the work on darkened Crookes tubes Rontgen observed on Nov. 8, 1895, the glimmering of barium platinum-cyanide crystals and discovered it was the consequence of unknown rays to which he gave the name X-Rays. At the end of the same year Rontgen gave a lecture about his discovery and in an unbelievably short time the entire world was informed about Rontgen's works⁽⁶⁶⁾.

During this time Tesla intensively studied the X-rays and his study results he published in ten articles between March 11, 1896, and Aug. 11, 1897⁽⁷⁾. On Apr. 6, 1897, he gave a lecture on his works related to Rontgen rays⁽¹⁷⁾ and showed a number of pieces of equipment for the device for the purpose of powerful X-ray production. In that lecture Tesla gave the interesting data on his previous studies of the operation of Crooke's tube in 1894. He observed then that some tubes which produced poorly visible light, influenced the sensitized photographic plate more powerfully than other tubes which produced visible light of higher level.

Tesla's studies were directed towards achievement of real phosphorescent light ("cool light") so that he delayed for some time, detailed examination of the mentioned event, as well as the cause of the appearance of various spots and the blurred photographic plates which were in the laboratory for a certain period of time after use. When he started to work on these problems, a fire occurred in the laboratory in which almost all the devices were destroyed (Mar. 13, 1895). Several months passed before he continued working on his studies and in the meantime, Rontgen published his discoveries. When Tesla found that, it was immediately clear to him what occured in his laboratory. Tesla repeated Rontgen's experiments, which were very briefly described, and he realized that he had made a mistake by not following certain observations he made during his studies with Crookes tubes.

During 1897-1898 Tesla performed many experiments with Rontgen rays. He was thinking about the nature of these rays and considered that they were caused by "particles or vibrations which are considerably above any frequency we are able to produce by capacitor discharge". He immediately observed the importance of high-voltage for the purpose of powerful ray production and suggested the application of his tubes with one electrode connected to the arcing oscillator secondary. It is interesting that Rontgen in the same month that Tesla published his first article, pointed to the great advantage in using Tesla's high frequency oscillator for X-ray production during a lecture to the Wurzburg Medical Society. Tesla performed X-ray refraction and transmission measurements on several metals, lead-glass, liscone and ebony. It is not certain however that he actually measured the refracted rays' intensity or that it was a question of secondary ray emission. Tesla attempted to prove the phenomenon of refraction, but he was not successful due to now understandable reasons. In his works and in his lecture at the American Science Academy, Tesla showed a series of tube designs for the production of power X-rays, most of which are similar to Leonard tubes (which Tesla frequently mentions), but without anode terminal.

June 7

Descriptions of the high-frequency transformer are to be found in Tesla's publications and patents from 1891 onwards^{(15, 4)}, but he did not patent it until 1897⁽²⁶⁾. The invention protected by this patent is “A transformer for developing or converting currents of high potential, comprising a primary and secondary coil, one terminal of the secondary being electrically connected with the primary, and with earth when the transformer is in use, as set forth”. It in particular protects the spiral form of the secondary, and a conical form is also mentioned. For ordinary uses a cylindrical secondary divided into two parts is proposed. A new feature is the specification that the length of the secondary should be “approximately one quarter of the wavelength of the electrical disturbance in the secondary circuit, based on the velocity of propagation of the electrical disturbance through the coil itself”, or, in general, “so that at one terminal the potential would be zero and at the other maximum”.

June 7

Already in 1891 a description of a high frequency transformer is mentioned in Tesla's works and patents^(4,15), but he patented it as late as 1897⁽¹⁶⁾. In this patent the discovery of ".... transformer for production or conversion of high voltage currents which consists of primary and secondary coil with one secondary terminal electrically connected to primary, and with grounding when the transformer is used as mentioned...". The secondary in the shape of a spiral is particularly protected, and a cone shape is mentioned as well. For the usual applications he suggest the cylindrical secondary divided into two parts. New information is that the secondary has to have the length of approximately ¼ wavelength determined on the basis of phenomenon propagation speed through the secondary or generally such length that the voltage at the open secondary terminal is maximum.

The primary coil of Tesla'a high frequency transformer almost always has one to two turns. Even with such a small number of turns the primary coil inductances are sufficiently large regarding the dimensions of these coils. For example, in his patent - "Electrical Energy Transmission System"⁽¹³⁾ the mentioned diameter of primary coil amounts to approximately 244 cm, and its inductance is approximately 8000 cms. He decided to use an even larger coil, which can be seen on the basis of data (radius 762 cm!).

In his note, Tesla does not talk about work on the laboratory construction and what he notes are the ideas and the data necessary for the experimentation. So, for example, now he describes the measurement of inductance by means of a balanced bridge, but he doesn't give the equation of the balance, and consequently some claims (and schematic) could not be proven with assurance.