​​Thomson's tube: the glass vacuum vessel used by the English scientist Joseph Thomson in his experiment on the properties of cathode rays

​​Thomson's tube is a glass vacuum vessel which the English scientist Joseph Thomson used in his experiment on the properties of cathode rays. In my day this was covered in the school physics course, and attention was usually drawn to the fact that the cathode-ray tubes of television sets were built on the pattern of this tube, though nowadays such television sets are no longer even made.

A high-voltage source was connected on the left; below is the anode (+), and the plate is the hot cathode (-); in the middle are the plates of a capacitor, with coils set at either side of them; into the third chamber, onto a screen (which is absent here), a beam was fired from the "gun" at the start, through another electrode with an aperture, between the capacitor plates and the inductance coils. Observing the deflection of the beam when there was no current in the coils and no voltage on the capacitor, Thomson established that the particles emitted were negatively charged. His next conclusion was that the specific charge of these particles is approximately the same in different gases, which in the end led him to the thought that the "substance" obtained from hydrogen and carbon is of one kind, and that all the elements are probably built from it. It was roughly thus that in 1897 the future Nobel Prize laureate discovered the existence of electrons.

PS The magnitude of the electron's charge was determined later, in 1910-1913, almost simultaneously by the American physicist Robert Millikan and by the Russian-Soviet scientist, the celebrated Academician Abram Fyodorovich Ioffe.