A stoker developed in Germany and used increasingly in that country and in the United States. The hearth consists of a rigid water-cooled matrix. Coal is fed on to this at one end and is moved across it by the vibrating motion to discharge as ash at the other end. The vibrations, with an amplitude of about 1/8 in (3 mm) and in progress for about 5 s every 2 min give a satisfactory feed rate. The rate of feed is controlled by altering the duration of the vibrations.