Page:Elementary Text-book of Physics (Anthony, 1897).djvu/407

§ 321] The first explanation is supported by certain facts known with regard to the changes that go on in the tube as the discharge is kept up through it, but it is otherwise unsatisfactory. Most of the facts known are consistent with the theory of short transverse vibrations, but no explanation of their origin is given. The theory of longitudinal vibrations has been to some extent developed by Jaumann; he assumes that the characteristic factor of the dielectric, which we have called the dielectric constant, is not really constant, but variable, and a function of the electromotive force. He then shows that on this assumption the electrical discharge in rarefied gases may set up longitudinal waves, and that these waves possess many, if not all, of the properties of the cathode discharge. Since the properties of the cathode discharge and of the Rontgen radiance are not the same, we cannot conclude that the latter are explicable by longitudinal waves, though there is as yet no evidence to the contrary.