Thomson Reveals Electron

On 30 April 1897, J.J. Thomson announced the discovery of subatomic particles of electricity (the electron) at the Friday Evening Discourse of the Royal Institution, in London, England.

Thomson was born outside Manchester, England, in 1856 and entered Trinity College, Cambridge University in 1876. He remained a part of the college for the rest of his life, rising from student to professor of physics.

Thomson wrote a series of well-received physics texts early in his career, including his Treatise on the Motion of Vortex Rings in 1884. He also wrote the Notes on Recent Researches in Electricity in Magnetism in 1892, which synthesized work performed after James Clerk Maxwell’s famous Treatise and has been called the “third volume of Maxwell.”

Towards the end of the century, Thomson began an original study of cathode rays that led to his discovery of the electron. He found that cathode rays were made of a previously unknown negatively charged particle. Previous scholars had thought that atoms were built of something smaller, but did not think this fundamental unit would be smaller than the smallest atom, hydrogen.

Thomson measured the size of cathode rays by comparing the heat generated when the rays hit a thermal junction with the magnetic deflection of the rays. Based on these measurements, Thomson proposed that this basic particle was more than one thousand times lighter than a hydrogen atom.

Thomson was awarded the 1906 Nobel Prize in Physics for his discovery of the electron.