In 1881, 55-year-old Irish physicist George Johnstone Stoney (1826–1911) presented his historic paper to the Royal Dublin Society, published in Philosophical Magazine (1881) under the title “On the Physical Units of Nature”.

Stoney calculated the world’s first quantitative estimate of the elementary electric charge ($e$) from Faraday’s laws of electrolysis and introduced the name “Electron” to designate the fundamental atomic quantum of electric charge.

Derivation of the Elementary Charge ($e$)

Stoney combined Michael Faraday’s 1833 electrolysis constant with Johann Josef Loschmidt’s 1865 estimation of Avogadro’s number ($N_{\text{A}}$):

1. Faraday Electrolysis Relation

The charge $Q$ required to liberate one mole of a monovalent ion (such as $\text{H}^+$ or $\text{Ag}^+$) is given by Faraday’s constant ($F \approx 96,485\,\text{Coulombs/mol}$):

$$F = N_{\text{A}} \cdot e \implies e = \frac{F}{N_{\text{A}}}$$

2. Stoney’s Value

Using the 1881 estimates for Avogadro’s constant, Stoney calculated:

$$e \approx 10^{-20}\,\text{Coulombs} = 10^{-10}\,\text{esu}$$

Although slightly smaller than the modern exact value ($e \equiv 1.602176634 \times 10^{-19}\,\text{C}$), Stoney’s calculation proved that electricity is not a continuous fluid, but exists as discrete, fundamental quantum units.

Coining the Term “Electron” (1891)

In 1891, Stoney formally published the term “Electron” in Scientific Transactions of the Royal Dublin Society:

“These definite quantities of electricity, which may be called electrons, are the fundamental unit charges of nature.”

When J.J. Thomson discovered cathode ray subatomic corpuscles in 1897, the physics community adopted Stoney’s term Electron for the particle itself.

Key Takeaways

  • Year: 1881
  • Key Figure: George Johnstone Stoney (Irish Physicist)
  • Core Discovery: Estimated elementary electric charge ($e = F / N_{\text{A}}$) and coined the term “Electron”.
  • Atomic Electricity: Proved electric charge is quantized in discrete physical units.
  • Quantum Relevance: Fundamental charge $e$ forms the coupling constant of Quantum Electrodynamics (QED).