Are Roentgen Ray Phenomena Due to Sound Waves?

The observations of Mr. Edison, recorded in his article in The Electrical Engineer of April 8, do not appear to me to warrant the conclusion at which he arrives. It is well known that sound shadows are not as sharply defined as light shadows and the reason is that the wave lengths of sound are very great compared to those of light. The shorter the wave lengths the sharper should be the shadows; that is, the less should the geometrical shadow be encroached upon by the radiant energy. Now the geometrical shadows for apparatus arranged as in Edison’s Fig. 1 would be included between the lines a a'. Rays deflected into the shadow, as shown in that figure, could not have been due to a true diffraction, but must have been due to some other cause.

The experiments of Le Conte, to which Mr. Edison refers, so far from warranting the conclusion that Edison draws from his own experiment seem to me to show that Edison’s result could not be due to diffraction, and therefore has no bearing upon the question as to the nature of the Röntgen radiations. Le Conte’s experiments show comparatively sharp sound shadows. Even at a distance of twelve feet from the pile, only one foot in diameter, casting the shadow, there was no apparent penetration within the geometrical boundary. If any such effect as Edison shows had occurred, the shadows should have been completely obliterated at one foot behind the pile.

The beautiful experiments of Professor Stine and of Scribner and M’Berty indicate a straight line propagation of the Röntgen radiations, and go far to prove that the result obtained by Edison must have been due to some other cause than that to which he ascribes it. These experiments were admirably adapted to demonstrate the source of the Röntgen rays, and led us back to the conclusion originally announced by Röntgen himself, which has always seemed to me to be the true one, notwithstanding all the different conclusions that have been drawn from later experiments. These results go to show how carefully Röntgen had studied the phenomena before making his original announcement.

These experiments seem to demonstrate conclusively that the source of the Röntgen radiations is the bombarded surface of the glass. It is probable, as suggested by Professor Elihu Thomson, that this bombardment produces two effects, one the Röntgen radiations and the other phosphorescence of glass, and that the greater the phosphorescence, the less the Röntgen rays.

I have always wondered why some of the various experimenters upon these phenomena have not made experiments to demonstrate, first, whether the Röntgen radiations are propagated as waves, or are flying particles shot off from the source, and, second, if waves, what is the wave length? If they are wave motions, whether the vibrations are longitudinal or transverse, the fact should be capable of demonstration by diffraction phenomena. Professor Snow, of the Wisconsin University, has suggested a method by which the test could be made.

A parallel beam of rays might be obtained by allowing the vibrations to pass successively through two narrow slits in lead screens placed a little distance apart. This beam being received upon a grating consisting of finer copper wires laid parallel to each other, should, if the radiations are wave motions, give diffraction phenomena that would demonstrate the fact, and also furnish data for computing the wave length, if the radiations consist of a few definite wave lengths only. The question whether those radiations are wave motions or an actual translation of particles, seems to me the most important one to be settled at this stage of the investigation, and I hope some one will take the matter up.