In the first place, when these rays fall on a substance they produce changes physical or chemical in the nature of the substance. I shall confine myself this evening to endeavoring to give an account of some of the more recent investigations which have been made on the cathode rays. Recently a great renewal of interest in these rays has taken place, owing to the remarkable properties possessed by an offsprings of theirs, for the cathode rays are the parents of the Röntgen rays. Crookes, whose experiments, by their beauty and importance, attracted the attention of all physicists to this subject, and who not only greatly increased our knowledge of the properties of the rays, but by his application of them to radiant matter spectroscopy has rendered them most important agents in chemical research. The physicist, however, who did more than any one else to direct attention to these rays was Mr.
Goldstein seems to have been the first to advance the theory, which has attained a good deal of prevalence in Germany, that these cathode rays are transversal vibrations in the ether. If the cathode were replaced by a luminous disk of the same size, this disk would not cast a shadow of a small object placed near it, for though the object might intercept the rays which came out normally from the disk, yet enough light would be given out sideways from other parts of the disk to prevent the shadow being at all well marked. This was a very important observation, for it showed that the rays casting the shadow came in a definite direction from the cathode. This observation was extended by Goldstein, who found that a well marked, though not very sharply defined, shadow was cast by a small body placed near a cathode of considerable area. The subject was next taken up by Plücker’s pupil, Hittorf, who greatly extended our knowledge of the subject, and to whom we owe the observation that a solid body placed between a pointed cathode and the walls of the tube cast a well defined shadow. Plücker ascribed these phosphorescent patches to currents of electricity which went from the cathode to the walls of the tube and then for some reason or other retraced their steps. Plücker, who had made a very minute study of the effect of a magnetic field on the ordinary discharge which stretches from one terminal to the other, distinguished the discharge which produced the green phosphorescence from the ordinary discharge by the difference in its behavior when in a magnetic field. He owed the opportunity to do this to his fellow-townsman Geissler, who first made such vacua attainable. Plücker was the first physicist to make experiments on the discharge through a tube in a state anything approaching what we should now call a high vacuum. To illustrate the effects of an electric field on a charged particle.The first observer to leave any record of what are now known as the cathode rays seems to have been Plücker, who in 1859 observed the now well-known green phosphorescence on the glass in the neighborhood of the negative electrode.To commemorate the discovery of the electron by J.As a result of his work, Thomson proposed a completely new model of the atom (Thomson’s Plum Pudding Model) that one of his students, Ernest Rutherford, would improve upon 10 years later.Ĭlick and drag the cursor to change the intensity of the voltage applied between the plates. This apparatus constitutes the first particle accelerator.
Thomson, in 1897, isolated a new elementary particle carrying a negative charge – the electron. The very intense electric field that results from this accelerates the few ions present in the tube which, via collisions, ionize other particles. The lower the pressure, the more the electrons thus liberated and accelerated travel great distances until they strike the screen at the opposite end of the tube.īy studying the deviation of this beam, J. A high voltage (between 10 and 100 kV) is applied between two electrodes. Thomson’s second experiment involving the deviation of an electron beam in a vacuum tube, called a Crookes Tube.Ī partial vacuum (less than 10 -6 atm) is maintained in the tube.