ABSTRACT
In 1883 Heinrich Hertz performed experiments on cathode rays in order to determine whether these rays carry an electric charge (Hertz 1896). In one experiment he separated cathode rays from ordinary electricity produced in a cathode tube and caused the cathode rays to enter an electrometer that would determine the presence of electric charge. In his experiment no electrical effect was produced. In a second experiment he introduced oppositely electrified plates into the tube to see if the cathode rays were deflected electrically. No deflection was produced. Hertz concluded, mistakenly as it turns out, that cathode rays carry no electric charge and hence are not composed of charged particles. His mistake, as J. J. Thomson (1897) showed experimentally fourteen years later, was to assume that the air in the cathode tube was sufficiently evacuated to allow electrical effects to occur. Thomson demonstrated those effects, concluded that the rays are indeed composed of electrically charged particles (later called “electrons”), and experimentally measured their ratio of mass to charge. (For his experiments with cathode rays Thomson received the Nobel Prize in 1906; he is credited with the discovery of the electron.) Concentrating just on Hertz’s negative experimental results in 1883, are (or were) these results evidence that cathode rays are electrically neutral? Several different answers are possible.
