J.J. Thompson Discovered the Electron — And Unknowingly Electrified Science Forever

When J.J. Thomson stood before the Royal Institution in 1897 to share his latest findings, few in the audience likely realized just how much physics was about to change. The particles he described — tiny, negatively charged “corpuscles” — would soon be known as electrons, according to a study in Nature.

And although their discovery marked a turning point in modern science, the journey to that moment wasn’t quite the eureka breakthrough textbooks sometimes describe.

The discovery of the electron wasn’t a lightning bolt from above. It was a slow burn built atop decades of experiments, theoretical guesswork, and even clumsy hands in a finely tuned lab. While J.J. Thomson gets much of the credit, his achievement was largely a product of his environment during an era of intense curiosity about the nature of electricity and matter.

J.J. Thompson and Subatomic Corpuscles

By the late 1800s, the scientific world was buzzing with questions about electricity and light. Several researchers were chasing phenomena that would eventually converge on the idea of the electron. And while Thomson is often credited as the ultimate discoverer of the electron, even that title is up for debate.

“Historians of science disagree on who actually ‘discovered’ the electron,” says Jaume Navarro, Ikerbasque research professor at the University of the Basque Country and author of A History of the Electron: J.J. and G.P. Thomson. “[M]any people working on electricity-related areas reached conclusions that might be regarded as the first experimental or theoretical instance of the modern electron: Zeeman, Lorentz, Lenard, and Larmor are the main actors in this story. So J.J. would only be one piece in this puzzle of constructing the electron.”

Thomson’s key insight came in 1897, when a series of innovative, highly tuned experiments helped him determine that tiny subatomic “corpuscles” might carry electricity itself.

“In 1897, he announced that the best explanation for the interaction between matter and electricity would be the ‘by no means impossible hypothesis’ that ‘electrified corpuscles’ of matter would be the unit carriers of electricity,” Navarro says. And it was only “when he tried to measure the charge-to-mass ratio of such corpuscles that he came to the conclusion that these corpuscles were probably smaller than the smallest atom.”

Read More: The X-Rays Thought to Prove What Makes Up Dark Matter Don’t, In Fact, Prove the Connection

Bending Particle Beams

Thomson’s famous cathode-ray experiments that revealed the electron seem deceptively simple today. He shot a beam of particles through a vacuum tube and used electric and magnetic fields to bend the particle beams. By varying the strength of these fields and tracking how the beam deflection angle changed, he could determine the particle’s charge-to-mass ratio. And he found it to be orders of magnitude smaller than any known atom.

“The experimental setup looks simple, but it was not,” Navarro says. “[T]he skills to have perfect tubes in which to have stable vacuum was not available to everyone at the time.”

In fact, Thomson’s success was largely attributable to the top-tier infrastructure of his lab and his own insights. The Cavendish Laboratory at Cambridge, where he became director in 1888, was already becoming a world-class hub of experimentation. Thomson was known to be “very clumsy,” Navarro says. But his lab assistant, Ebenezer Everett, was very skilled in glass blowing, capable of producing the high-quality vacuum tubes that were crucial for Thomson’s experiments, according to Science Museum, U.K.

The Electron Discovery

Popular science often frames great discoveries as “eureka” moments. But that doesn’t quite fit here.

“We tend not to like ‘eureka’ moments because they tend to be oversimplifications of complex processes,” Navarro says. In Thomson’s case, the true spark came from an entirely different discovery: X-rays.

“The real disruptive element did not depend on [Thomson]: it was the discovery of the Röntgen rays (X-rays) that really made him and many other physicists turn their attention to them,” Navarro says. “JJ was working with discharge tubes filled with gases, and X-rays happen in the vacuum. So, it was X-rays that made him change his experimental setup.”

Even the scientific community took years to rally around the electron as real.

“Actually, even the existence of atoms was still controversial among some physicists and, especially, chemists in the late 1800s,” Navarro says. “So, a sub-atomic ‘corpuscle’ was a challenge.”

It wasn’t until decades later that Thomson was widely regarded as the discoverer of the electron.

“His 1906 Nobel Prize was granted ‘in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases,’” Navarro says, “not for any specific discovery, let alone the electron (which he kept calling the corpuscle).”

Set Up to Succeed

As director of the Cavendish Laboratory, Thomson’s influence went well beyond his own research.

“His directorship of the Cavendish laboratory allowed him to follow and direct many researchers at the time,” says Navarro. “Moreover, his Cambridge training helped, but also prevented him in his work,” due to a prevailing belief in the continuity of matter and the ether.

In fact, Thomson’s faith in the continuous nature of matter endured for decades, even as quantum theory began to reshape physics. “By the time he published [his 1907 book The Corpuscular Theory of Matter], his dream of having the electron as the only elementary particle, i.e., as the ‘prime matter’ of all material substances, was over,” Navarro says. “But he said that such corpuscular theory was ‘a policy, not a creed.’”

Fittingly, it was Thomson’s own son, G.P. Thomson, who would later prove electrons could also behave as waves, helping usher in the quantum revolution.

After the Spark

Thomson didn’t have everything figured out when it came to the internal structure of the atom, though. For instance, he pursued the “plum-pudding” model of the atom, a term Navarro notes Thomson never used.

After ‘discovering’ the electron and realizing they couldn’t account for the majority of the mass of an atom, Thomson “tried (unsuccessfully) to find positive ‘corpuscles’ with a similar experimental setup,” Navarro says.

Failing to find any relevant results, “he kept thinking that positive electrification was distributed throughout the ether in the atom, with corpuscles situated in stable arrangements within this sea of positively electrified ether,” Navarro says.

Nonetheless, Thomson’s original “corpuscle” would go on to ignite entire fields of science and industry. And more than a century later, the electron remains one of the most thoroughly studied and best-understood particles in the universe. Still, its origin story highlights the true, messy, collaborative, and often contradictory history of scientific discovery.

Read More: Advanced Quantum Material Curves the Fabric of Space

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