On J.J. Thompson

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were needed to resolve the uncertainties. When physicists moved a magnet near the glass, they found they could push the rays about. Nevertheless, when the German physicist Heinrich Hertz passed the rays through an electric field created by metal plates inside a cathode ray tube, the rays were not deflected in the way that would be expected of electrically charged particles. Hertz and his student Philipp Lenard also placed a thin metal foil in the path of the rays and saw that the glass still glowed, as though the rays slipped through the foil. Did that not prove that cathode rays were some kind of waves?
Other experiments cast doubt on the idea that these were ordinary particles of matter, for example gas molecules as some suggested. In France, Jean Perrin had found that cathode rays carried a negative charge. In Germany, in January 1897 Emil Wiechert made a puzzling measurement indicating that the ratio of their mass to their charge was over a thousand times smaller ...

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that the atom was indivisible, the most fundamental unit of matter.
Thomson's speculation was not unambiguously supported by his experiments. It took more experimental work by Thomson and others to sort out the confusion. The atom is now known to contain other particles as well. Yet Thomson's bold suggestion that cathode rays were material constituents of atoms turned out to be correct. The rays are made up of electrons: very small, negatively charged particles that are indeed fundamental parts of every atom.
But, do atoms have parts? J.J. Thomson suggested that they do. He advanced the idea that cathode rays are really streams of very small pieces of atoms. Three experiments ...

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