Abstract: A variable electric capacitor has two electrode units consisting of a plurality of plates or a single spirally wound plate with several turns. The plates or turns have opposite lateral edges, one of which is free and the other is fixed to a support. The plates or turns of the two electrode units are interleaved and to change their mesh, one electrode unit is movable relative to the other. Each electrode unit has locating elements for the free lateral edge of plate or turn of the other electrode unit. These locating elements adjoin the supports of the electrode unit concerned and are formed to hold the free lateral edge of each plate or turn of the other electrode unit in a predetermined position when both electrode units are in their maximum mesh position.

Abstract: Apparatus for obtaining extra- and/or intra-oral dental X-ray photographs comprising an X-ray tube having an anticathode with a plane target surface inclined with respect to the cathode-ray axis. The anticathode is disposed in a small tube within an X-ray-permeable protective sleeve. For changing the mode of operation from extra-oral to intra-oral, an adapter is fitted over the protective sleeve and actuates a change-over switch disposed within the housing of the X-ray tube. Regulating means control the intensity of the cathode-ray depending upon the position of the change-over switch for making either extra- or intra-oral photographs.