Art. LVII.—Refraction and Reflexion of x-rays.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 29, 1896, Unnumbered Page

Art. LVII.—Refraction and Reflexion of x-rays. By Dr. W. P. Evans. [Read before the Philosophical Institute of Canterbury, 30th November, 1896.] While taking an x-ray photograph of a set of chemical weights a very unlooked-for result was obtained. The weights were of the cylindrical pattern, and had exceptionally well-polished surfaces. They were placed in two

rows, one on each side of the x-ray tube, and at varying lateral distances, so that the angle of incidence of the rays varied considerably throughout the series. In the case of those farthest from the tube, and where, therefore, the angle of incidence was comparatively large, nothing but the well-defined and highly-distorted shadow was obtained. Where, however, the angle of incidence was small, the side of the shadow nearest the tube was bordered by a dense crescent shaped band, varying in thickness from nil to 0·8mm. The experiment was repeated, and the same result obtained. The sharpness and extent of this reflexion crescent depended on the temperature of the tube and the angle of incidence. A common brass set gave no such reflexion effect, probably because their surfaces, though smooth in, the ordinary sense of the word, were rough compared to those of the highly-polished platinum. A gilded weight gave a slight image as long as it was dry. In consequence of this experiment some of Röntgen's earlier experiments were repeated, with the result that glass in the form of powder showed a distinctly greater absorbing-power than the same mass in sheet form. If there were no reflexion or refraction of the rays at the faces of the small pieces of glass the powdered glass and the original plate should both have the same effect. These experiments tend to show that the x-ray vibrations are probably transverse, and of extremely short period.