Page:Popular Science Monthly Volume 67.djvu/15

Rh plate in a vacuum, but no appreciable charging was observed. The $$\beta$$ rays were temporarily got rid of by heating the radium in order to drive off its emanation. There was found to be a strong ionization set up at the surface from which the rays emerged and the surface on which they impinged. The presence of this ionization causes the upper plate to rapidly lose a charge communicated to it. Although this action would mask to some extent the effect to be looked for, a measurable difference should have been obtained under the experimental conditions, if the a rays were expelled with a positive charge; but not the slightest evidence of a charge was observed. I understand that similar negative results have been obtained by other observers.

This apparent absence of charge carried by the $$\alpha$$ rays is very remarkable and difficult to account for. There is no doubt that the a particles behave as if they carried a positive charge, for several observers have shown that the a rays are deflected by a magnetic field. It is interesting to notice, in this connection, that Villard was unable to detect that the 'canal rays' carried a charge. These rays, discovered by Goldstein, are analogous in many respects to the $$\alpha$$ rays. They are slightly deflected by a magnetic and electric field and behave like positively charged bodies atomic in size. The value of $$e/m$$ is not a constant, but depends upon the nature of the gas in the tube through which the discharge is passed. The apparent absence of charge on the a particles may possibly be explained on the supposition that a negatively charged particle (an electron) is always projected at the same time as the positively charged particle. Such electrons, if they are present, should be readily bent back to the surface from which they came by the action of a strong magnetic field. It will be of interest to examine whether the charge carried by the $$\alpha$$ rays can be detected under such conditions. Another hypothesis, which has some points in its favor, is that the a particles are uncharged at the moment of their expulsion, but, in consequence of their collision with the molecules of matter, lose a negative electron and consequently acquire a positive charge. This point is at present under examination. The question is in a very unsatisfactory state and requires further investigation.

It is remarkable that positive electricity is always associated with matter atomic in size, for no evidence has been obtained of the existence of a positive electron corresponding to the negative electron. This difference between positive and negative electricity is apparently fundamental, and no explanation of it has as yet been forthcoming.