Report of Superintendent. 61 



Tliese engines were all of the horizontal, non-condensing type, and 

 were each constructed with some form of the side frame, now so 

 universally adopted. The chief differences consisted in the mechan- 

 ism, by means of which the point of cut-off was automatically adjusted 

 by the governor ; also, the cylinder of the Babcock and Wilcox engine 

 was steam jacketed, which was not the case with either of the other 

 engines. 



As is well known, the Corliss engine has independent steam and 

 exhaust valves placed near the ends of the cylinder ; the two steam 

 valves at the top, and the two exhaust valves at the bottom. The 

 valves are segmental, working in the bottom of circular valve chests, 

 and are operated by rock arms on central spindles, which receive, 

 from a vibrating plate, the so-called " wrist motion " peculiar to the 

 Corliss engine. The point of cut-off is regulated by disengaging 

 the valve by means of the governor, at any time before half-stroke, 

 and closing it by a weight, checked, after a partial descent, by an air 

 cushion. 



The Babcock and Wilcox engine has a long slide valve working 

 over ports, located in the side of the cylinder, and leading direct into 

 the clearance at each end. The cut-off" consists of two plates sliding 

 over openings through the main valve, which plates are operated by 

 the piston of a small steam cylinder. The cut-off' takes place when- 

 ever steam is admitted to the small cylinder, and the time at which 

 this occurs is varied by the governor, which changes the angular 

 position of a small crank operating the valve of the small cylinder. 

 The Rider engine has also a common slide valve. The cut-off 

 Talve stem moves along behind and parallel with, the main valve, 

 and carries two cylindrical cut-off valves, the outer ends of which are 

 cut on spiral lines. The back of the main valve is hollowed out in 

 semi-cylindrical shape, to make a seat for the cut-off valves, and 

 steam ports pass angularly through it, with the edges terminating on 

 spiral lines corresponding to the ends of the cut-oft* valves. The 

 latter receive motion from a separate eccentric, and the cut-off" is 

 varied by simply turning the cut-off stem a little, and thus changing 

 the time at which the spiral ends of the valves meet the correspond- 

 ing ports. This is done in a simple manner by the governor. Since 

 the cut-off" valves are moved in a longitudinal direction by the engine, 

 the least force applied in a tranverse direction, by turning the stem, 

 serves to direct the valve face from its direct course, and it moves 

 over its seat in a diagonal line, on the principle of the composition 



