The vats were superseded by what are called _engines_, a Dutch invention well adapted to the purpose. The engines are sometimes arranged in pairs on different levels, the bottom of one being higher than the top of the other, so that the contents of the higher engine may be let off into the lower. In the upper engine, called the _washer_, the rags are first worked coarsely with a stream of water running through them to wash and open their fibres: this reduces them to what is called _half stuff_; they are then let down into the _beating_ engine to be ground into pulp fit for making paper. Each engine consists of a large wooden vat or cistern V V, Figs. 3, 4, of oblong figure on the outside, with the angles cut off; the inside, which is lined with lead, has straight sides and circular ends. Or the vat may be entirely formed of cast-iron. It is divided by a partition P P, also covered with lead. The cylinder C is firmly fixed to the spindle _s_, which extends across the engine, and is put in motion by the pinion _w_, which engages other wheels set in motion by water or steam-power. The cylinder is of wood, but is furnished with a number of teeth or cutters attached to its surface parallel with the axis, and projecting about an inch from it. Immediately below the cylinder is a block of wood B, also furnished with cutters, so that when the cylinder revolves its teeth pass very near those of the block, the distance between them being regulated by elevating or depressing the bearings _l l_, on which the necks of the spindle _s s_ are supported. These bearings are made on two levers _l l_, which have tenons at their ends fitted into upright mortises made in stout beams bolted to the sides of the engine. The levers _l l_ are movable at one end of each, the other ends being fitted to rise and fall on bolts in the beams as centres. The front one of these levers, or that nearest the cylinder C, can be raised or lowered by turning the handle of the screw; the cylinder is thus made to cut coarser or finer by enlarging or diminishing the space between the two sets of cutters. At one part of the vat is a breasting B', made of boards and covered with sheet lead, curved to the form of the cylinder and nearly in contact with its teeth. An inclined plane I, passes from the bottom of the vat to the top of the breasting which terminates in the block B. The vat is supplied with water from the mill-dam by means of pumps worked by the water-wheel. The water is first discharged by the pipe P, Fig. 4, into the cistern _c_, the supply being regulated as occasion may require. A grating covered with a hair strainer is fixed across the cistern to prevent any solid impurity from passing into the vat; or the water may be strained through a flannel bag tied over the mouth of the pipe P, as shown in the figure. The vat being full of water and a quantity of rags put in, the cylinder is set in motion, the effect of which is to produce a