1850: Geissler, a German scientist, demonstrated the flow of electric current through a vacuum glass tube.

1878: Sir William Crookes, a British scientist, showed how current in vacuum tubes appears to consist of particles.

1890: Perrin, a French physicist, demonstrated that current in vacuum tube is due to the movement of negatively charged particles.

1897: Sir J. J. Thomson, a British physicist, measured some of the properties of the “negatively charged particle” (cathode ray) contributing to current in vacuum tube (named as cathode ray tube). He concluded that these particles are much smaller than atoms possessing high specific charge (charge to mass ratio). Thus, he is credited with the discovery of the first sub-atomic particle (later named as electron).

1904: John Ambrose Fleming, a British physicist, invented vacuum tube that allows current only in one direction. This was named as Fleming valve- the primitive version of a diode- and was also known as vacuum tube or vacuum diode.

1907: Lee de Forest, an American scientist, invented a tube which could amplify weak electrical AC signal. This tube, a primitive version of the transistor, was named as vacuum triode.

1909: Robert Millikan, an American physicist, measured the charge of an electron.