"When a current of electricity from an induction coil or influence machine is sent between two metal electrodes fused into the ends of a glass tube (say 12 inches long) from which the air is gradually withdrawn by a pump, the tube presents a continuous succession of striking appearances" (Kaye 1914,1). The electric eggs - 169 and 170 - from which air could be removed using an air pump, were used to demonstrate the effects, the latter incorporating an electro-magnet in order to show the relative motion of an electric discharge around a magnetic field.
At a sufficiently low vacuum there is a dark space between the electrodes, and the glass walls of the tube begin to glow. In due course it was discovered that the glow was caused by a stream of "cathode rays", later named "electrons", emanating from the negatively charged electrode (the cathode). The name electron was coined in 1891 by an Irishman George Johnstone Stoney (1826-1911), who played an important part in the studies which led eventually to the physical discovery of the electron around 1917 by Englishman Sir J.J. Thomson (1856-1940) (O'Hara 1993).
While the nature of cathode rays was still unclear, the German Wilhelm Röntgen (1845-1923) made a related discovery in 1895. He found that, when the cathode rays in an evacuated tube hit a solid target, another kind of ray could be detected outside the tube, even when it was covered in an opaque shield of black cardboard. He called these rays "X-rays" because of uncertainty about their nature. They turned out to be electromagnetic waves, that is light of short wavelength. The light we see is only part of the electromagnetic spectrum, which extends from gamma rays, through X-rays, ultra-violet, visible, infra-red, microwave, to short medium and long radio waves. The X-rays are now well known because of their medical use. Bone, flesh and foreign bodies are not transparent to them to the same extent, and they can thus be used to "see through" flesh (Mollan 1992,57). Röntgen received the first Nobel prize, awarded in 1901.
X-ray tubes soon became increasingly sophisticated, and those in the collection represent some of the earlier developments of the tubes.

169 Electric Egg

Elec./Mag. Page

Voltameters