J. J. Thomson and the electron
In his famous paper, Cathode Rays (published in The Electrician on May 21st 1897), J. J. Thomson starts by acknowledging the significant work that was done before him; pointing out that it was first Julius Plücker who observed the green glow of a cathode ray tube, then Heinrich Geissler who greatly improved vacuum systems, and finally Johann Hittorf and Eugen Goldstein who first explored ways to casts shadows from these rays. All four individuals were German; those were the glory days of a unified Germany under Bismarck. All of that is well and good, but Thomson affirms that it was William Crookes (a Brit) who “did more than any one else” with the “beauty and importance” of his experiments to advance the field and draw interest to it… JJ was a Brit too. He proceeds, introducing photoluminescence, thermoluminescence, x-rays, etc. and only then, after paying homage to the giants before him, he dares to enter new territory. His most important observation is the fact that these cathode rays deflect the same amount when a magnet is placed near them regardless of the density of the gas used—defying intuition. And most importantly, that this circular path could be described “by negatively electrified particles projected with great velocities”, but he struggles to separate the particles from the rays they emit (i.e. electron beams vs light rays). He comes extremely close to equating them: “I think, the stream of negatively-electrified particles is an invariable accompaniment of the cathode rays.” The paper then distracts itself by inconsequential experiments, vacillates between the rejection or acceptance of the hypothesis of these being charged particles, and even misrepresents x-ray emissions with cathode rays. But right at the end the tone changes, and he invites us to suppose they are indeed particles (or corpuscles, as he called them) and dares measure the ratio of their mass to the charge carried by them. Finding his answer, he points out that the number “is very small compared with the value for the ratio of the mass of an atom of hydrogen [sic] to the charge carried by it”. He had taken the first known measurement of an electron!
Unlike his hero, Thomson doesn’t end the paper with a poem (unfortunately), but it does leave humanity with a new single-letter variable: e, the charge of an electron. At the annual Cavendish dinner, a triplet immortalized JJ’s success:
The corpuscle won the day
And in freedom went away
And became a cathode ray
Source: Thomson, J. J. Cathode Rays. The Electrician - A weekly illustrated journal of electrical engineering industry and science 39, 104–109 (1897).
Public Domain
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Full disclosure, I may occasionally borrow a sentence from Will Durant's Story of Civilization. I absolutely love that collection!