William Crookes observed the luminous stream, later named as cathode rays, during his experiment using his invention known as the Crooke’s tube. While experimenting with the cathode-ray tube, incidentally Crookes noted that undeveloped photographic plates could be sensitized when placed near his vacuum tube. Therefore in spite of such peculiar observation he was not aware that such photochemical phenomenon could be related with the radiation originated from such rarefied tube.

Fig. 350 - An early type of X-Rays apparatus
The history of science has many subtle situations as similar to Crooke, another well-known physicist, Philip Lenard, did not pay attention to investigate the fluorescent behavior of a thin aluminum foil covered with a layer of barium platinocyanide when hit by the cathodes rays originated from nearby Crooks tube.
Wilhelm Conrad Roentgen was a mechanical engineer graduated at Zurich Federal Polytechnic Institute in 1868. Even considering he had never studied Physics he graduated with PhD through his work about the “Study on Gases”.
Considering his great interest in Physics experiments as well as due to his studies in exploring the behavior of the cathode ray led him to work with others researchers as: Hertz, Hitttorf and Crookes, and soon he was able to prove the effect of those rays in sensitizing photographic plates.
On November 8, 1895, Roentgen repeated the experiments conducted by Lenard using a Crookes tube provided with a type of mask.
Working in his home laboratory he noted that part of the cathode rays generated was escaping from tube passing through the mask. Following Lenard experiment he placed a thin aluminum plate covered with a layer of barium platinocyanide near the Crookes tube, observing that the invisible cathode rays had been escaped through the mask and in this way caused a fluorescent effect on the same.
It occurred to Roentgen that it might be advisable to open a window in the thick glass wall of the Crookes tube in order to allow the flow of the cathode rays. Considering the cathode rays were invisible Roentgen noted it would be necessary to use a kind of screen to detect their flow. Therefore, since the cathode rays flow could be lower in the nearby wall glass tube rather than the ones originated from the opened window covered with thin aluminum strips, due to the intensive luminosity in the Crookes tube probably it would be impossible to observe the feeble fluorescence in the screen.
Fig. 350A - In Germany, Geissler was a forerunner in the manufacturing of vacuum tubes provided with electrodes when connected to an electrostatic machine or induction coil were able to generate luminous discharged.
In this way to avoid all the undesired environment luminosity he covered the Crookes tube with the black cardboard hood as well as he darkened the laboratory room.
When applying charges on the Crookes tube he observed a vivid gleaming yellow-greenish outflow. Astonished Roentgen repeated the experiment for several times and finally he concluded that the fluorescence arisen was due to an unknown type of ray, which he temporarily termed as X-Rays. Fig 350
In the reality the X-Rays are a type of electromagnetic wave allocated in a portion of the radio frequency spectrum consisting in a quick changing either in the electromagnetic and force fields.
Just after the discovery of the X-Rays the future researches were concentrated for medical application, primarily for orthopedic diagnosis purpose only.
As usual in many discoveries the first years were conducted in a trial and error basis considering either the precariousness of the equipment used as well the X-Rays behavior in the human beings was still unknown.
Fig. 351 - A modern radiation generator, as know as X-Rays tube.
Therefore, due to the continuous researches after the second half of XX century, it was possible to develop new types of radiation generators as known as X-Rays tubes, following to an improved calculation for proper dosing control. Fig 351
Thus to obtein good quality roentgenogram of the bone’s tissues the X-Rays apparatus should be setup for low voltage and current, around 70 kV.
Further to new development in the radiological techniques, the same started to be used for diagnosis purposes in other medical areas such as: gastroenterology, pneumatology. When diagnosing thorax maladies, for instances, pulmonary phthisis, considering the areas under evaluation are either in movement or even in deeper cavities it was mandatory that the radiation generator should operate in high tension and for short exposition time arisen new techniques trends as the development of the fluoroscopy.
Based on such technological advancements, precision X-Rays machines were launched in the market and when operating with enhancing techniques physicians could detect with high accuracy fractures, growth and many others difficulty in finding diseases.
The Roentgen’s discovery has been considered the greatest application of the electrical phenomena in the modern medical science and certainly it was the forerunner of the radiology as well as the image diagnosis led to the invention in 1972 of the sophisticated computed axial tomography.
As aforementioned, the discovery of the X-rays was deeply related with the advancements in the study of Electricity at the end of the XX century and in this way gave birth to new fields of researches as the ones for high accurate measuring and recording of the feeble biological electrical currents.