Abstract: A mineral mining installation has a longwall scraper-chain conveyor with a machine, such as a plough, guided for movement back and forth alongside the conveyor to win mineral from a longwall face. A roof support system which may be arranged at the ends of the longwall working, i.e., at the so-called stable zones, is composed of several units each with hydraulic props protected within cylindrical telescopic casings. Each support unit may be displaceable as a whole to follow the working progress or else each support unit may be constructed with front and rear frame assemblies which are relatively displaceable. Each support unit has at least five narrow elongate roof bars disposed closely side-by-side in parallelism. The roof bars are guided for longitudinal advancement and hydraulic rams serve to advance the roof bars individually or in groups. A similar arrangement may also be employed as the floor structure of each support unit.

Abstract: A novel method for detecting charge on large bodies such as the earth is accomplished by means of disclosed apparatus which includes a vertical column of mercury having an associated electrode which is capacitively coupled to the mercury column when the mercury level is above the position of the electrode. By establishing an initial unipotential state for the apparatus by short circuit connection of the electrode and mercury column to the earth and an electrometer connected between the electrode and the earth which is initially short-circuited across its terminals the apparatus is conditioned to sense the charge of the large body to which it is connected (the earth) by moving the mercury column up and down past the position of the electrode with the electrometer open-circuited and thus connected between the electrode and earth during the passage of the mercury in one direction past the electrode.

Abstract: In a color pickup tube for use in a single tube or two tube type color television camera system wherein an optical color analyzing stripe filter, a transparent film, a transparent electroconductive film and a photoconductor film are disposed in the order mentioned on the rear side of the transparent glass substrate of the tube, the thickness of the transparent film is increased gradually from the central portion toward the peripheral portion of the transparent film.