There is of course no longer anything unknown about the nature of X-rays.
They are electromagnetic radiation of exactly the same nature as visible light.
Except that their wavelength is several orders of magnitude shorter.
This conclusion follows from comparing properties 1 through 4 with the similar properties of visible light but it was actually postulated by Thomson several years before all these properties were know Thomson argued that X-rays are electromagnetic radiation because such radiation would be expected to be emitted from the point at which the electrons strike the wall of a cathode ray tube
At this point the electrons suffer very violent acceleration in coming to a stop and according to classical electromagnetic theory all accelerated charged particles emit electromagnetic radiations.
We shall see later that this explanation of the production of X-rays is least partially correct