Are Röntgen Rays Polarised?

Abstract

MR. L. CASELLA has made for me a Crookes' tube having as the anode a platinum window sealed into the end of the tube opposite the kathode, which is the ordinary aluminium disc. Owing to the glass sealing, only a small portion of the platinum, about 3 mm. in diameter, is free to act. The light from all but this portion was screened off by thick glass discs and a brass disc, these having each an aperture in the centre. The result, with the fluorescent screen, was at first poor, because the vacuum was too low; but as that got higher it improved, and I was able to electrograph a part of the hand, by the rays given off by this small platinum window, in 15 seconds, the plate being 2½ from the window. An ordinary focus tube takes 30 seconds to produce the same effect under similar conditions, but gives better definition. With the platinum window tube, though the bones are defined on the fluorescent screen, there seems to be too much white light, and the difference between bones and flesh is less marked. The tilted platinum of a focus tube, apparently, reflects most of the kathode rays, but transmits some. Compare the behaviour of the platinum in both tubes with the action of 9 light on glass. With both glass and platinum, part of the rays are transmitted and part reflected, the proportion varying with the angle of incidence; but, with both, those rays which are perpendicular are apparently transmitted. If the glass be tilted at the proper angle, the reflected rays and a small part of the transmitted rays are polarised. Suppose the plate of glass in the position of the platinum window, and the source of light a luminous point within the tube; although most of the transmitted light would be radiated direct from the luminous point, part would be rays which had been polarised by reflection from the walls of the tube. The analogy would still hold good, for we know that, as far as X-rays are concerned, glass behaves very similarly to platinum, for these rays are under suitable conditions given off by both.