Ideas: A History of Thought and Invention, from Fire to Freud

by Peter Watson

But it was Thomson’s 1897 discovery which capped everything, produced the first of the Cavendish’s great successes and gave modern physics its lift-off, into arguably the most exciting and important intellectual adventure of the modern world. In a series of experiments J. J. pumped different gases into the glass tubes, passed an electric current, and then surrounded them either with electrical fields or with magnets. As a result of this systematic manipulation of conditions, Thomson convincingly demonstrated that cathode ‘rays’ were in fact infinitesimally minute particles erupting from the cathode and drawn to the anode. Thomson further found that the particles’ trajectory could be altered by an electric field and that a magnetic field shaped them into a curve.10 More important still, he found that the particles were lighter than hydrogen atoms, the smallest known unit of matter, and exactly the same whatever the gas through which the discharge passed. Thomson had clearly identified something fundamental–this was in fact the first experimental establishment of the particulate theory of matter.