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Geissler discovered cathode rays in 1855

J.J. Thomson measured the charge-to-mass ratio of the cathode rays in 1897, and so recognised them as particles ....electrons.

Millikan measured the charge on the electron in 1909

 Timeline

1836
Nicholas Callan (Priest in Maynooth) invented the Induction Coil (for high voltages)
1855
Geissler invented a good vacuum pump
1855
Plucker and Geissler observed fluorescence in a gas discharge tube.
1867
Hittorf identified the cathode as being responsible for the glow
1868
Crookes discovered that cathode rays were deflected by magnetic fields.
1876
Goldstein confirmed Hittorf’s view and introduced the name “cathode rays”.
1884
Thomas Edison discovered thermionic emission.
1891
George Stoney (Irish scientist) named the smallest quantity of electricity as an electron.
1895
Jean Perrin (French scientist) proved that cathode rays were negatively charged particles.
1897
J.J. Thomson measured the charge-to-mass ratio of the electron.
1899
J. J. Thomson
(England, 1856-1940)
showed that the Edison effect is due to electrons .
1909
Robert Millikan (American scientist) measured the charge on tiny oi-droplets and hence deduced the charge on the electron.
1913
Rutherford proposed that electrons orbited a nucleus in an atom (like planets around a sun).
1927
Heisenberg Heisenberg’s uncertainty principle explained the difficulty of knowing where an electron is at any moment
1933
Dirac (English physicist) predicted the existence of an anti-particle for the electron.