ABSTRACT
When Wilhelm Conrad Rontgen discovered X-rays he was investigating the conduction of electricity in gases at low pressures, i.e. gas discharges. However, gas discharge is not necessary for the production of X-rays: the requirement is for high speed electrons to be stopped or slowed suddenly. If the tube was too 'hard' there was a danger of puncturing the tube and making it useless for X-ray production. If alternatively the tube was too 'soft' then the X-rays would lack the penetrative power to obtain a good contrast radiograph. Tube design was thus based on the principle that such substances as caustic potash, palladium and potassium permanganate, when placed in an auxiliary glass bulb of low vacuum, liberate gases when heated and reabsorb the gases upon cooling. When the tube ran properly, the main bulb B was filled with a brilliant green light, with a sharp cut zone through the plane of the platinum anode A.
