CHAP, v.] THE STEAM-ENGINE. 397 



obviously in these that the greater part of the heating takes place, and 

 hence they are appropriately called heaters. 



The two figures indicate with sufficient clearness the positions 

 and dimensions of the furnace, the grate and the ashpit, on which no 

 more need be said. 



With regard to the chimney, its base is seen at u, and we can 

 follow the course of the smoke and the gases of combustion, from their 



FIG. 274. Boiler, with heaters (exterior view). 



origin in the fire to the chimney bottom, through flues c c, which 

 pass between the heaters and the boiler. 



The position of these flues must be taken note of. The one 

 below the heaters causes the flame and the heated gases to pass to the 

 end of the furnace and heat the heaters themselves directly. From 

 thence the gases mount by one of the two upper lateral flues, and 

 part with a portion of their heat to the boiler with which they come 

 in contact. And lastly, a third passage conducts them through 

 another flue, to escape up the chimney. 



