X-rays

After the Crookes tube is excited by the coil the magnetic lines of force are projected down in the same manner as they pass off from a magnet, and traversing the intervening space, pass through the body down to the floor, and back to the coil and tube again, completing the circuit. The X-ray is electrostatic in character and of a very high potential. With every discharge from the Crookes tube oxygen is liberated in the body, as well as the surrounding atmosphere, which, combining with nascent oxygen, forms ozone. It is due to the electrolysis produced in the body that we are able to destroy the bacilli in contagious disease, ozone being the most powerful germicide known.

— George M. Sternberg, 'Science and Pseudo-Science in Medicine, Science, N.S. V (110), 199–206, 5 February, 1897. Paper Read before the Anthropological Society of Washington, December 15, 1896.

If the discharge of a fairly large induction coil be made to pass through a Hittorf vacuum tube, or through a Lenard tube, a Crookes tube, or other similar apparatus, which has been sufficiently exhausted … and if the whole apparatus be placed in a completely darkened room, there is observed at each discharge a bright illumination of a paper screen covered with barium platinocyanide, placed in the vicinity of the induction coil …
— Wilhelm Konrad Röntgen (1845 – 1923), describing how he discovered X-rays.

The most striking feature of this phenomenon is that an influence capable of exciting brilliant fluorescence is able to pass through the black cardboard cover, which transmits none of the ultra-violet rays of the sun or of the electric arc, and one immediately enquires whether other bodies possess this property. It is soon discovered that all bodies are transparent to this influence, but in different degrees. A few examples will suffice. Paper is very transparent, the fluorescent screen held behind a bound volume of 1000 pages still lighted up brightly; the printer’s ink offered no perceptible obstacle.

Fluorescence was also noted behind two packs of cards; a few cards held between apparatus and screen made no perceptible difference. A single sheet of tinfoil is scarcely noticeable. Only after several layers have been laid on top of each other is a shadow clearly visible on the screen …

Glass plates behave differently, depending on whether they contain lead (flint glass) or not; the lead-free ones are much less transparent than the others. If the hand is held between the discharge tube and the screen, the dark shadow of the bones is visible within the slightly dark shadow of the hand…

A wooden rod, 20 x 20 mm cross-section, painted white, with lead paint on one side, behaves in a peculiar manner. When it is interposed between apparatus and screen, it has almost no effect when the X-rays go through the rod parallel to the painted side, but it throws a dark shadow if the rays have to traverse the paint. Very similar to the metals themselves are their salts, whether solid or in solution.
— Wilhelm Konrad Röntgen (1845 – 1923), A new kind of rays — Eine Neue Art von Strahlen, paper presented to the Physico-Medical Society of Wurzburg, 1896.

[Of the Wilson cloud chamber] In a recent communication, I described a method of making visible the tracks of ionising particles through a moist gas by condensing water upon the ions immediately after their liberation. At that time I had only succeeded in taking photographs of the clouds condensed on the ions produced along the tracks of alpha-particles and of the corpuscles set free by the passage of X-rays through the gas. The interpretation of the photographs was complicated to a certain extent by distortion arising from the position which the camera occupied.

The expansion apparatus and the method of illuminating the clouds have both been improved in detail, and it has now been found possible to photograph the tracks of even the fastest beta-particles, the individual ions being rendered visible. In the photographs of the X-ray clouds the drops in many of the tracks are also individually visible; the clouds found in the alpha-ray tracks are generally too dense to be resolved into drops. The photographs are now free from distortion. The cloud chamber has been greatly increased in size; it is now wide enough to give ample room for the longest alpha-ray, and high enough to admit of a horizontal beam of X-rays being sent through it without any risk of complications due to the proximity of the roof and floor.
— Charles Thomson Rees Wilson (1869 – 1959), Proceedings of the Royal Society, 1912, A, 87, 277.

Moseley’s rules

1. Every element from aluminium to gold is characterised by an integer N which determines its X-ray spectrum. Every detail in the spectrum of an element can therefore be predicted from the spectra of its neighbours.

2. This integer N, the atomic number of the element, is identified with the number of positive units of electricity contained in the atomic nucleus.

3. The atomic numbers for all elements from Al [aluminium] to Au [gold] have been tabulated on the assumption that N for Al is 13.

4. The order of the atomic numbers is the same as that for the atomic weights, except where the latter disagrees with the order of the chemical properties.

5. Known elements correspond with all numbers between 13 and 79 except three. There are three possible elements still undiscovered.
— Henry Gwyn-Jeffreys Moseley (1887 – 1915).

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