X-rays can penetrate many solid substances such as construction materials and living tissue, [ 4 ] so X-ray radiography is widely used in medical diagnostics e. Their generation and use is strictly controlled by public health authorities. X-rays were originally noticed in science as a type of unidentified radiation emanating from discharge tubes by experimenters investigating cathode rays produced by such tubes, which are energetic electron beams that were first observed in Early researchers noticed effects that were attributable to them in many of the early Crookes tubes invented around Crookes tubes created free electrons by ionization of the residual air in the tube by a high DC voltage of anywhere between a few kilovolts and kV.
This voltage accelerated the electrons coming from the cathode to a high enough velocity that they created X-rays when they struck the anode or the glass wall of the tube. The earliest experimenter thought to have unknowingly produced X-rays was William Morgan. In , he presented a paper to the Royal Society of London describing the effects of passing electrical currents through a partially evacuated glass tube, producing a glow created by X-rays.
Starting in , Philipp Lenard conducted experiments to see whether cathode rays could pass out of the Crookes tube into the air. He built a Crookes tube with a "window" at the end made of thin aluminium, facing the cathode so the cathode rays would strike it later called a "Lenard tube".
He found that something came through, that would expose photographic plates and cause fluorescence. He measured the penetrating power of these rays through various materials. It has been suggested that at least some of these "Lenard rays" were actually X-rays. Helmholtz formulated mathematical equations for X-rays.
He based it on the electromagnetic theory of light. Goodspeed were making photographs of coins with electric sparks. On 22 February after the end of their experiments two coins were left on a stack of photographic plates before Goodspeed demonstrated to Jennings the operation of Crookes tubes.
