What’s an electron, anyway?

An electron is one of those tiny negative particles, right? Well, that’s not how things were originally.

The word itself comes from the greek for amber (ήλεκτρον) because that’s how people first noticed the phenomena of charged objects. For some reason, scientists throughout time have been obsessed with rubbing various objects with cat fur to see what happened.

I’ve been reading the 1917 book “The Electron” by Robert Millikan (of the oil drop fame). He identifies George Stoney (in 1891) as the person who first suggested the word. However, this was in the days before anyone had identified an electron as a distinct object. When Stoney used the word ‘electron’ he defined it to be a “unit of electricity, namely that quantity of electricity which must pass through a solution in order to liberate .. one atom of hydrogen”. So, in 1891, Stoney wasn’t talking about the electron as a ‘thing’ but as an amount of charge, which today we’d measure as coulombs.

At some point the meaning must have changed, presumably after JJ Thomson discovered his ‘corpuscles’ in 1897 and Millikan measured the charge on them around 1909.

However, I was surprised to read the following line in the later chapters of the Millikan book:

“We have concerned ourselves with studying the properties of these electrons themselves and have found that they are of two kinds, negative and positive, which are however, exactly alike in strength of charge but wholly different in inertia or mass”

So it seems that in 1917 the word ‘electron’ was being used to collectively refer to what we now call electrons and protons. I have no idea of exactly when the meaning finally shifted to the modern version.