546 THE STEAM-ENGINE. 



completely from the priming. The wider part of the great steam-pipe a is 

 flanged and screwed at the hinder end to a corresponding aperture in the back 

 plate of the fire-box. This opening is covered by a circular plate, secured by 

 screws, having a stuffing-box in its centre, of the same kind as is used for the 

 piston-rods of steam-cylinders. Through this stuffing-box the spindle a" of 

 the regulator passes, and to its end is attached a winch A', by which the 

 spindle a" is capable of being turned. This winch is limited in its play to a 

 quarter of a revolution. The other end of the spindle a" is attached to a plate 

 e', seen edgewise in fig. 67, and the face of which is seen in fig. 72 ; this cir- 

 cular plate e' is perforated with two apertures somewhat less than quadrants. 

 That part of the plate, therefore, which remains not pierced forms two solid 

 pieces somewhat greater than quadrants. This plate is ground so as to move 

 in steam-tight contact with a fixed plate under it, which terminates at the wide 

 end of the conical mouth of the steam-pipe S. This fixed circular plate is 

 likewise pierced with two nearly quadrantal apertures, corresponding with 

 those in the moveable plate e' . When the moveable plate e' is turned round by 

 the winch h 1 , the apertures in it may be made to correspond with those of the 

 fixed circular plate on which it moves, in which position the steam-pipe S 

 communicates with the funnel d' by the two quadrantal apertures thus open. 

 If, on the other hand, the winch h' be moved from this position through a 

 quarter revolution, then the quadrantal openings in the moveable plate will be 

 brought over the solid parts of the fixed plate on which it moves, and these 

 solid parts being a little more than quadrants, while the openings are a little 

 less, all communication between the steam-pipe S and the funnel d' will be 

 stopped, for in this case the quadrantal openings in the fixed and moveable 

 plates respectively will be stopped by the solid parts of these plates. It will 

 be evident that as the winch h' of the regulator is moved from the former 

 position to the latter, in every intermediate position the aperture communicating 

 between the funnel d' and the steam-pipe S will be less in magnitude than 

 the complete quadrant. It will in fact be composed of two openings having 

 the form of sectors of a circle less than a quadrant, and these sectors may 

 be made of any magnitude, however small, until the opening is altogether 

 closed. 



By such means the admission of steam from the boiler to the steam-pipe S 

 may be regulated by the winch h 1 . 



The steam being admitted to the steam-pipe passes through it to the front 

 end of the boiler, and the pipe being enclosed within the boiler the temperature 

 of the steam is maintained. The steam-pipe passing through the tube-plate 

 at the front end of the boiler is carried to a small distance from the tube-plate 

 'in the same direction, where it is flanged on to a cross horizontal pipe pro- 

 ceeding to the right and to the left as represented in fig. 74. This cross pipe 

 is itself flanged to two curved steam-pipes, S, fig. 74, by which the steam is 

 conducted to the valve-boxes V V. The lower ends of these curved arms are 

 flanged on to the valve-boxes of the two cylinders at the ends nearest to the 

 boiler. The opening of one of these is exhibited in the right-hand cylinder 

 in fig. 69. By these pipes the steam is conducted into the valve-boxes or 

 steam-chests, from which it is admitted by slide-valves to the cylinders to 

 work the pistons in the same manner as has been already described in the 

 large stationary engines. 



On the upper sides of the cylinders are formed the steam-chests or valve- 

 boxes, which are exhibited at U, figs. 67, 69, 74. These are made of cast- 

 iron half an inch thick, and are bolted to the upper side of each cylinder. At 

 the front end they are also secured by bolts to the smoke-box, and at the 

 hinder end are attached to the tube-plate. These valve-boxes communicate 



