WRINKLING OF FILM When a film wrinkles at the edges it is known as frilling (which see). When the whole of the film is wrinkled in wavy lines the defect is known as reticulation (which see).
An iodised collodion to which is added a tincture of powdered turmeric giving to it a rich yellow colour. Positives are made with it on black glass, giving an effect like a gilded daguerreotype.
(Fr., Rayons X ; Ger., ..Y-Strahlen, Rontgen-Strahlen) Prof. Röntgen, in 1895, discovered certain rays, to which he gave the name of X-rays, and he investigated their action on the sensitive emulsion of the dry plate. X-rays are pro duced by the discharge of a high-potential current through a special form of vacuum tube, known as a Crookes' tube (which see). The positive terminal of an induction coil or Wims hurst machine is connected to the anode and the negative to the cathode of the tube. The anticathode is connected to the anode and is also positive. The vacuum of a tube is not perfect, and the current is conveyed through the tube by the infinitesimal quantity of air contained therein.
The " cathodal rays " which pass from the cathode to the anticathode consist of infinite simal particles travelling at a high rate of speed ; when the progress of these minute bodies is arrested, X-rays are produced. The green fluorescence on the sides of the tube opposite the anticathode, though not caused by the X-rays, demonstrate their presence.
The X-rays are ethereal vibrations travelling with much the same velocity as light. They travel in a straight line in all directions from the point of origin, and are almost incapable of reflection or refraction.
X-rays are invisible to the eye, but have the property of rendering fluorescent certain sub stances—for example, calcium tungstate and barium platino-cyanide. When a screen coated with these substances is placed near the X-ray tube in a darkened room, the tungstate or barium surface emits a fairly bright fluorescence. If an object such as the hand or a lead pencil is placed between the screen and the tube, the denser parts (the bones or the graphite) appear as black shadows in a grey background.
X-rays penetrate all substances to a greater or less degree, although heavy metals, such as lead and mercury, are, for photographic or visual purposes, practically opaque to the rays.
The greater part of X-ray examination is conducted by photographic methods, as the image given by the rays on a dry plate or film show far more detail than can be seen by visual examination with the fluorescent screen.