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Roentgen rays or X-rays

The discovery of X-rays


During 1895 Wilhelm Conrad Röntgen was investigating the external effects from the various types of vacuum tube equipment — apparatuses from Heinrich Hertz, Johann Hittorf, William Crookes, Nikola Tesla and Philipp von Lenard — when an electrical discharge is passed through them. In early November, he was repeating an experiment with one of Lenard's tubes in which a thin aluminium window had been added to permit the cathode rays to exit the tube but a cardboard covering was added to protect the aluminium from damage by the strong electrostatic field that is necessary to produce the cathode rays. He knew the cardboard covering prevented light from escaping, yet Röntgen observed that the invisible cathode rays caused a fluorescent effect on a small cardboard screen painted with barium platinocyanide when it was placed close to the aluminium window. It occurred to Röntgen that the Hittorf-Crookes tube, which had a much thicker glass wall than the Lenard tube, might also cause this fluorescent effect.


Wilhelm Conrad Röntgen (1845-1923)
Wilhelm Conrad Röntgen (1845-1923)


Today we know that X-radiation (composed of X-rays) a form of invisible, high frequency electromagnetic radiation. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to with terms meaning Röntgen radiation, after Wilhelm Röntgen, who is usually credited as its discoverer, and who had named it X-radiation to signify an unknown type of radiation


They are produced by accelerating electrons at a metal target. In  medical  application,  this  is  Tungstran  (95%),  Rhenium  (5%),  or Molibden. X  rays  are  used  in  various  medical  application.


X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds. This makes it a type of ionizing radiation, and therefore harmful to living tissue. A very high radiation dose over a short amount of time causes radiation sickness, while lower doses can give an increased risk of radiation-induced cancer. In medical imaging this increased cancer risk is generally greatly outweighed by the benefits of the examination. The ionizing capability of X-rays can be utilized in cancer treatment to kill malignant cells using radiation therapy. It is also used for material characterization using X-ray spectroscopy.




An early Crookes x-ray tube from a museum dedicated to Wilhelm Conrad Roentgen in Würzburg, Germany (image used under the terms of GNU Free Documentation License)



Tesla and the discovery of the X-rays


Twain and Tesla became friends in the 1890s, thanks in part to Twain’s lifelong fascination with technology and new inventions. Visiting Tesla’s lab late one night, Twain posed for one of the first photographs to be lit by incandescent light. In 1895, Tesla and photographer Edward Ringwood Hewett invited Twain back to the lab to pose for another photo, this one lit using an electrical device called a Crookes tube. When Tesla reviewed the resulting photographic negative, he found it splotchy and spotted and decided it was ruined. It was only weeks later, after German scientist Wilhelm Röntgen announced his discovery of what he called “X-radiation” produced by Crookes tubes, that Tesla realized the photograph of Twain had been ruined by the X-ray shadows of the camera’s metal screws.


The Electrical Review in 1896 published X-rays of a man, made by Tesla, with X-ray tubes of his own design. They appeared at the same time as when Roentgen announced his discovery of X-rays. Tesla never attempted to proclaim priority and much of his research was lost later in a fire at a New York warehouse.


Tesla had originally noticed what he described as "a very special radiation" years earlier when working his "carbon-button" lamp. He produced pictures he called "shadowgraphs" and had performed numerous experiments with them up until the fire at his lab. Upon learning of Röntgen's discovery, Tesla wrote him and sent some of the pictures recovered from the fire. Röntgen replied and asked Tesla how he produced them.


Roentgen congratulated Tesla on his sophisticated X-ray pictures, and Tesla even wrote Roentgen's name on one of his films. He experimented with shadowgraphs similar to those that later were to be used by Wilhelm Rontgen when he discovered X-rays in 1895. Tesla's countless experiments included work on a carbon button lamp, on the power of electrical resonance, and on various types of lightning. Tesla invented the special vacuum tube which emitted light to be used in photography.



Shadowgraph of a human foot in a shoe. Tesla obtained the image in 1896 with x-rays generated by his own vacuum tube, similar to Lenard's tube, at a distance of 8 feet. (Courtesy of the Tesla Museum, Belgrade, Serbia; document no. MNT,VI/II, 122.)



Roentgen’s letter to Tesla dated July 20th, 1901. The letter reads (Courtesy of the Tesla Museum, Belgrade, Serbia; document no. MNT, CXLIV, 152.):


“Dear Sir! You have surprised me tremendously with the beautiful photographs of wonderful discharges and I tell you thank you very much for that. If only I knew how you make such things! With the expression of special respect I remain yours devoted, W. C. Roentgen.”





In the list of the Nikola Tesla's many inventions may be found a variety of novel electric lamps, all of which were designed to operate in conjunction with specially designed high frequency power supply units. Some of these lamps were the forerunners of our present day fluorescent tubes. In fact, not long ago a small Californian company announced the development of a high frequency electronically powered fluorescent bulb, dubbed the E-Lamp, which bears a striking resemblance to a bulb that Tesla designed and built nearly one hundred years ago. The principal upon which they both work is identical. Another type of lamp was essentially the same as the slender neon filled tubes that are now commonly bent into the shapes of letters and used in storefront advertising. A third type of electric lamp that Tesla designed, known as the incandescent carbon button lamp, was capable of producing light at high levels of efficiency. A variation on the design of this lamp is embodied in the popular Plasma Globe novelty item. Another lamp that he patented in 1891 under the name "Electric Incandescent Lamp" has recently been adopted by the United States Armed Forces as part of a portable high intensity lighting system. The lamp itself consists of a spark gap enclosed within a small gas filled glass bulb.


Tesla's study of high voltage, high frequency alternating currents lead to the development of a large variety of vacuum tubes, some of which had medical applications.


He developed techniques for the generation of X rays and for their use to photographically image living tissue. One of his tubes has even been recognized as a primitive forerunner of the modern day electron microscope.


Tesla's discoveries also form part of the foundation of the medical discipline known as Nuclear Magnetic Resonance Imaging. In fact, in 1960 the official standard unit of magnetic flux density was designated the "tesla" thus placing him among an exclusive group of outstanding world-class scientists such as Volta, Ampere, Faraday, Kelvin, Roentgen and Curie.



Tesla displayed drawings of some 120 vacuum tubes and bulbs from which hundreds of devices were produced to illustrate lecture on X-rays and high frequency apparatus at The New York Academy of Sciences on April 6, 1897 in his lecture "The Streams of Lenard and Roentgen and Novel Apparatus for Their Production". The lecture was published by Leland I. Anderson, Editor. (The master of lighting Pg.77).





Tesla's experimental station at Colorado Springs. Shown is an ante room off the main experimental area. An X-ray photographic cabinet can be seen on the table, and underneath the table an electric heater. It should be pointed out that this was the only source of heat in the cold winter days from October to January 1900 when Tesla returned to New York City. 1899.






His work with the single terminal incandescent lamp led him to investigate other phenomena associated with vacuum tubes including the generation and physical properties of X rays. Tesla's more advanced tubes differ from typical X-ray tubes in that they have no target electrode and produce X rays through vacuum high-field emission and a process known as Bremsstrahlung. His work in this area set the stage for the development of high-energy particle accelerators. [Nikola Tesla: Lecture Before The New York Academy of Sciences, April 6, 1897]



Fig. ?
Fig. ?


Drawing illustrates Tesla’s unipolar vacuum tube, consisting of a glass bulb (b), a single electrode (e), and a lead-in conductor (c). The tube can be adapted for use with two electrodes by placing the second electrode at the levels indicated by the dotted lines. Published in Electrical Review, New , April 1, 1896.


Apart from experiments using the Crookes tube, Tesla invented his own vacuum tube (Fig ?), which was a special unipolar x-ray bulb. It consisted of a single electrode that emitted electrons. There was no target electrode; therefore, electrons were accelerated by peaks of the electrical field produced by the high-voltage Tesla coil. Even then, Tesla realized that the source of x-rays was the site of the first impact of the “cathodic stream” within the bulb, which was either the anode in a bipolar tube or the glass wall in the unipolar tube he invented. Nowadays, this form of radiation is known as Bremsstrahlung or braking radiation. In the same article, he stated that the cathodic stream was composed of very small particles (ie, electrons). His idea that the produced rays were minute particles wasn’t wrong at all; many years later, physicists described particle properties of electromagnetic radiation quanta called photons. To avoid heating and melting of the glass wall of his x-ray bulb, Tesla designed a cooling system based on a cold blast of air along the tube, as well as on today’s widely accepted oil bath surrounding the tube.



Tesla believed that everything we need to understand the universe is around us at all times, however in order to understand it real world devices had to be developed to augment our perception of existence. This line of thinking lead to Tesla laying the groundwork for modern X-rays. From Kirlian Photography to Wilhelm Rontgen’s discovery of the “X-ray”. Tesla began investigating X-rays using high voltages and tubes of his own design and worked with the output of a tesla coil.





Tesla's X-Ray tube, part of his method for utilizing "radiant energy," which operated from the top of a Tesla coil, providing a means to charge the "elevated insulated body of capacitance" C, with armatures T-T'.


"Whenever the circuit is closed owing to the rotation of the terminal t', the stored energy is discharged"


Tesla also experimented with reflected x-rays, using different materials as reflecting surfaces and describing features of transmitted and reflected rays. He thought that the practical purpose of the reflected x-rays was to improve the quality of the shadowgraph by increasing the object-film distance and decreasing exposure time. He was disappointed upon observing that lenses caused no refraction of x-rays. Later, it came to be understood that x-rays cannot be refracted by optical lenses due to their high frequency. However, Max von Laue managed to deviate x-rays using crystal lenses in 1912. Tesla explained changes in x-ray characteristics as being caused by variations in x-ray tubes and electrical generators. He correctly realized that strong shadows can be produced only at great object-film distances and with short exposure times. Moreover, he perceived that bulbs with thick walls produced rays with greater penetrating power, which was later explained by the longer deceleration of electrons on the thicker barrier.


Tesla was also among the first researchers to alert the scientific community on the biologic hazards of working with unipolar x-ray tubes, attributing the harmful effects on the skin to the ozone and the nitrous acid generated by the rays, rather than to the ionizing effects of the radiation. He described acute skin changes like redness, pain, and swelling, as well as late consequences such as hair loss and new nail growth. He compared sudden pain and irritation of the eyes while working with x-rays to the experience of stepping from a dark room into bright sunlight. This pain and irritation was considered to be the consequence of eyestrain due to long-lasting observation of the fluorescent screen in darkness. Tesla understood the three main elements of radiation protection: distance, time, and shielding. He discovered that adequate distance from the x-ray source was a useful safety factor. Instead of explaining the sudden diminution of the harmful effects of radiation on the basis of the inverse square law, however, he attributed it to lower ozone concentrations. Tesla advised people working at very short distances from the tube (eg, surgeons) to shorten the exposure time to a maximum of 2–3 minutes. He also tried to construct a protective shield made of aluminum wires connected to the ground.


On Hurtful Actions of Lenard and Roentgen Tubes- Electrical Review - May 5th, 1897


"The rapidly extending use of the Lenard and Roentgen tubes or Crookes bulbs as implements of the physician, or as instruments of research in laboratories, makes it desirable, particularly in view of the possibility of certain hurtful actions on the human tissues, to investigate the nature of these influences, to ascertain the conditions under which they are liable to occur and — what is most important for the practitioner — to render all injury impossible by the observance of certain rules and the employment of unfailing remedies.


As I have stated in a previous communication (see Electrical Review of December 2, 1896) no experimenter need be deterred from using freely the Roentgen rays for fear of a poisonous or deleterious action, and it is entirely wrong to give room to expressions of a kind such as may tend to impede the progress and create a prejudice against an already highly beneficial and still more promising discovery; but it can not be denied that it is equally uncommendable to ignore dangers now when we know that, under certain circumstances, they actually exist. I consider it the more necessary to be aware of these dangers, as I foresee the coming into general use of novel apparatus, capable of developing rays of incomparably greater power. In scientific laboratories the instruments are usually in the hands of persons skilled in their manipulation and capable of approximately estimating the magnitude of the effects, and the omission of necessary precautions is, in the present state of our knowledge, not so much to be apprehended; but the physicians, who are keenly appreciating the immense benefits derived from the proper application of the new principle, and the numerous amateurs who are fascinated by the beauty of the novel manifestations, who are all passionately bent upon experimentation in the newly opened up fields, but many of whom are naturally not armed with the special knowledge of the electrician — all of these are much in need of reliable information from experts, and for these chiefly the following lines are written. However, in view of the still incomplete knowledge of these rays, I wish the statements which follow to be considered as devoid of authoritativeness, other than that which is based on the conscientiousness of my study and the faith in the precision of my senses and observations".



Edison and Tesla corresponded in the 1890s over X-rays and may have worked together; we don't have Tesla's letters to Edison. However, it hardly seems the language or activity of mortal enemies.


Edison wrote to Tesla on 18 March 1896:


"My dear Tesla, Many thanks for your letter. I hope you are progressing and will give us something that will beat Roentgen."


In response to a critical essay to be published in the Electrical Review in May of 1896, Edison said he didn't care what the article stated for his own sake, but he added:


"Tesla is of a nervous temperament and it will greatly grieve him and interfere with his work. While Tesla gives vent to his sanguine expectations when he should not do so, it must not be forgotten by [the article author] Mr Moore that Tesla is an experimenter of the highest type and may produce in time all that he says he can."


That's hardly the language or activity of mortal enemies. However, it seems that the situation changed some years later when Edison became the partnership of Marconi and he criticized his idea of sending messages through the whole surface of the planet.


Tesla's Reply to Edison - English mechanic and world of science - July 14, 1905


A Bit of Sarcasm.


Permit me to say on this occasion that if there exist to-day no facilities for wireless telegraphic and telephone communication between the most distant countries, it is merely because a series of misfortunes and obstacles have delayed the consummation of my labors, which might have been completed three years ago. In this connection I shall well remember the efforts of some, unwise enough to believe that they can gain an advantage by throwing sand in the eyes of the people and retarding the progress of invention. Should the first messages across the seas prove calamitous to them, it will be a punishment regrettable but fully deserved.


The X-ray experiments were too dangerous, like Tesla had warned in some articles, and the radiation emitted caused cancer and nearly blinded Edison and ultimately killed his assistan Clarence Dally. He personally supported Dally's widow and children financially, and he never pursued X-ray research again. The event haunted him for the rest of his life, causing him to later remark:


“Don't talk to me about X-rays. I am afraid of them. I stopped experimenting with them two years ago, when I came near to losing my eyesight and Dally, my assistant practically lost the use of both of his arms. I am afraid of radium and polonium too, and I don't want to monkey with them."




The following list of quotes are related with Tesla's experiments on the production of X-rays.


Tesla’s Latest Results – He Now Produces Radiographs at a Distance of More Than Forty Feet - Electrical Review - March 18th, 1896:


"I am producing strong shadows at distances of 40 feet. I repeat, 40 feet and even more. Nor is this all. So strong are the actions on the film that provisions must be made to guard the plates in my photographic department, located on the floor above, a distance of fully 60 feet, from being spoiled by long exposure to the stray rays. Though during my investigations I have performed many experiments which seemed extraordinary, I am deeply astonished observing these unexpected manifestations, and still more so, as even now I see before me the possibility, not to say certitude, of augmenting the effects with my apparatus at least tenfold!"

"These effects upon the sensitive plate at so great a distance I attribute to the employment of a bulb with a single terminal, which permits the use of practically any desired potential and the attainment of extraordinary speeds of the projected particles. With such a bulb it is also evident that the action upon a fluorescent screen is proportionately greater than when the usual kind of tube is employed, and I have already observed enough to feel sure that great developments are to be looked for in this direction".


Nikola Tesla Talks Of The Future Of The Greatest Problems Now Confronting The Scientific World - New York Press - March 2, 1913


Q. What do you thing of radium and the prospect it opens for the future?


"My views on the subject are probably not in the agreement of those of many men of science who have devoted themselves to this branch of investigation. It may not be generally known that in my papers published in the electrical Rview in New Yorkvfrom 1896 to 1897, long before the discovery of Mm. Curie I demostrated the existence and described the salient properties of emanations of the same nature. My views were received with skepticism at that time, but I'm glad to say that now they are adopted in their enterity. I see no reason for changing the opinions I then expressed. The so-called radium emanations are not an insolated phenomenon, but are universal. There is, according to my ideas, no such element as radium or polonium, although spectral analisys, the theory of Mendeleff, and various experimental observations, support this modern view. I believe that as to this, scientific opinion is in error, as it was a century ago in assuming that there was such a substance as phlogiston concerned in combustion until Lavoisiere discovered oxigen. Similarly the radium manifestations are, in all probability, due to the action of a universal medium on certail volatile substance. Much of the spaculation based on Mm. Curie's is necesarilly erroneous, being in direct contradiction to well stablished principles. The claims of some enthusiasts that in radium lies the possibility of future power developement are nothing but a dream. But some fact is that we are in presence of new and wonderful effects the study of wich is leading us gradually to a better and deeper understanding of the mechanism of the universe".


Harnessing Nature - Can The Free Energy Of Space Be Utilized? - Scientific American - April 5, 1913


"Experiments conducted by Mr. Nikola Tesla with electromotlve forces of 2.000.000 volts have convinced him that if 100.000.000 volts could be produced it might be possible to break down the atomic structure of any element and thus liberate a certain amount of energy. "But," he told the wrlter of this artlcle, “even lf the feat could be accomplished and suficient energy set free, there still remains the enormously dificult problem of devising a means of utillzing the energy ln a practical way."


Tesla, 75, Predicts New Power Source - New York Times - July 5th, 1931


"When and where do you expect to make the official announcement of your new discoveries?" the inventor was asked.


These discoveries," he replied, "did not come to me over night, but as the result of intense study and experimentation for nearly thirty-six years. I am naturally anxious to give the facts to the world as soon as possible, but I also wish to present them in a finished form. That may take a few months or a few years.


The idea of atomic energy is illusionary but it has taken so powerful a hold on the minds, that although I have preached against it for twenty-five years, there are still some who believe it to be realizable.


I have disintegrated atoms in my experiments with a high potential vacuum tube I brought out in 1896, which I consider one of my best inventions. I have operated it with pressures ranging from 4,000,000 to 18,000,000 volts. More recently I have designed an apparatus for 50,000,000 volts which should produce many results of great scientific importance.


But as to atomic energy, my experimental observations have shown that the process of disintegration is not accompanied by a liberation of such energy as might be expected from the present theories.


And as for the cosmic ray: I called attention to this radiation while investigating Roentgen rays and radioactivity. In 1899 I erected a broadcasting plant at Colorado Springs, the first and only wireless plant in existence at that time, and there confirmed my theory by actual observation. My findings are in disagreement with the theories more recently advanced.


I have satisfied myself that the rays are not generated by the formation of new matter in space, a process which would be like water running up hill. According to my observations, they come from all the suns of the universe and in such abundance that the part contributed by our own sun is very insignificant by percentage. Some of these rays are of such terrific power that they can traverse through thousands of miles of solid matter".


A new Tesla coil for  X-ray work - Electrical review - July 22, 1896
A new Tesla coil for X-ray work - Electrical review - July 22, 1896


New Tesla Coil For X-Ray Work - Electrical review - July 22, 1896


A coil known as the modified Tesla coil has been placed upon themurkct by the L. E. Knott Apparatus Company, of 14 Ashburton Place, Boston, Mass. This coil contains many new features entirely different from anything before seen in the practical electrical Held. They have employed a new form of transformer, which lifts the current from 52 to about 35,000 volts. The principle of this transformer does not differ materially from that of the induction coil, except the ratio of the core to the primary and secondary is so adjusted that the principle of the regular alternating current transformer applies. Also, by a new method of insulation, the secondary coil is so wound that each layer is surrounded by au oil of high insulating properties. A new feature also has been introduced in the condenser since not only the transformer and oscillator, but also thc condenser itself, is immersed in oil. Great im- provement bas been made here in the condensing surface since the old method of using tinfoil has been discarded and and much more permanent copper plate substituted. By an arrangement of the primary of the transformer, also, either a 52 or 104- volt current can be used equally well. If the former, the machine will take six ainperes. If the latter, about three. When working on the number of watts here indicated, a steady discharge of something over eight inches is obtained. The frequency is so high that striking Tesla effects are also produced. Many of the experiments that are so ably discussed in Tesla’s little book can be shown with great satisfaction with the coil here described. It is not thought that the problem of running a high-frequency coil on a direct current has ever before been successfully solved. Wonderfully successful work. it is said, has been done by this coil so excited. The great improvement, however, on this coil is the mechanical spark gap which renders the discharge of the condenser absolutely uniform and the rapidity of the discharge under the control of the operator. As the manufacturers of these coils are in the physical and chemical apparatus business, and dealing with hospitals, it is but natural that they should endeavor to place a coil on the market which is especially adapted to this kind of work. We are pleased to know of their success and to know that the instruments have so far been developed that surgeons End them of great practical value.



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Comments: 1
  • #1

    Andre (Saturday, 12 March 2016 10:57)

    It is also interesting to note that due to the close proximity of the discovery that certain ores (eg pitchblende) affect film Tesla might actually have been on the road to discovering radioactivity either by accident (say, finding fogged film) or intentionally. I speculate that had that catastrophic fire not occurred his Physics Nobel would have been all but guaranteed.