EXPLANATION OF THE PLATES. 349 



PLATE XIX. 



In this plate, Fig. 1. is a section, and Fig. 2. a plan, of a steam boat engine. 

 A strong frame of cast iron supports the crank shaft I, and connects the parts of 

 the engine ; and the whole is sustained by two strong beams on the floor. The 

 steam pipe S brings the steam from the boiler to the passages of the slide, and 

 from thence to the top or bottom of the cylinder A, and it passes from the 

 slide to the condenser B, where it is condensed by a rose jet playing constantly ; 

 the air pump C expels the air and water into the cistern D, from whence it runs 

 out by a pipe. The motion of the piston is transmitted to the crank by means of 

 the double side beams or levers E F, moving on the axis G ; these are connected to 

 the cross head of the piston L L by two rods called the side rods, and the ends E 

 are connected to the crank by the connecting rod H. The air pump is also worked 

 by side rods from the side beams, and the hot water pump from the same cross 

 head. The parallel motion is guided by the radius rod M N ; see art. 489. : the 

 vibration of the beam is not bisected ; see page 233, note. The slide is on Mur- 

 doch's construction, (art. 447.) and is moved by a wheel on the crank shaft I, 

 with a sliding frame P, (art. 481.) and by hand by the lever T; the slide rod 

 being moved by slings from the arm R. The valve O is used to let steam into 

 the condenser in setting the engine to work, and the air and water are blown out 

 at the discharge valve into the cistern D. 



For the strength of the parts, see art. 496. ; the proportions of the engine, art. 

 419 422. The parts of the slide should be counterbalanced, in order that its 

 resistance may be equal in either direction. 



Each vessel generally has two of these engines, placed parallel to one another, 

 with a passage between them ; and there is room left for working the fires between 

 the cylinder and the boilers. The coals should be kept in iron tanks in the engine- 

 room, each to hold a given weight of coal, with the object of ascertaining with 

 accuracy the consumption for any time ; about four tons is a sufficient quantity to 

 be together, and they should be kept out of the danger of taking fire. 



The proportion of the power to the effect is given in Sect. x. art. 655. 



