Wilhelm Conrad Röntgen: the X-rays discovery

In 1894 Wilhelm Conrad Röntgen, professor at the University of Würzburg, started his experimental research on cathode rays, discovering an unknown radiation able to pass through the objects. In 1895 he realised the first medical X-ray and in 1901 was awarded the Nobel Prize for Physics. Röntgen donated the prize amount to his university and never patented his discovery, deeply convinced that "every discovery belongs to the whole humanity".

The recreation of the experimental system by means of which Wilhelm Conrad Röntgen discovered the X-rays. On repeating the Philipp Lenard's experiments, Röntgen used a large Ruhmkorff inductor coil (device 3) with a Deprez switch, applying a primary current of circa 20 A. This supplied energy to a Lenard vacuum tube (device 4), connected to a Raps vacuum pump. This device generated "sparks of appropriate length" which have been impressed on a nearby barium platinocyanide screen.

The power supply in Wilhelm Conrad Röntgen's experiments was a rechargeable battery.

The photo shows the Ruhmkorff's inductor coil (device n. 3) and, on the left, the Deprez switch. The induction coil was widely used to excite rarefied gas tubes (such as the Lenard tube) for the spectroscopic study, through X-rays. The device consists of a Deprez switch, named after its inventor, placed between the accumulator and the primary winding of the Ruhmkorff's inductor coil. As a whole, the device is an electrical transformer used to produce electrical impulses. The secondary winding is connected to the Lenard tube that emits X-rays.

The glass element is the Lenard tube, i.e. the X-rays emitter, which is the evolution of the Crookes tube. It consists of a glass bulb, inside which a high vacuum is created. It contains an emitter of cathode-rays which collide against a thin layer of aluminum, called "Lenard window", generating the X-rays emission

The gases rarefaction inside the Lenard X-ray tube is achieved through a mercury vacuum pump, invented by August Raps in 1891. This device, derived from the "Geissler-Toepler" pump, is equipped with an automatic mercury flow control system, composed of the interrupters placed on the right (5). A similar system was widely used to create vacuum in the industrial production of light bulbs.