and the Economy of Fuel. 161 



by double brick walls. These walls are expressed in 

 the following figure. 



Fig. 1 8. This is a horizontal section of the fire-place 

 at a level with the bottom of the boiler, a, a, a, a, are 

 four openings by which the flues which, in the first 

 arrangement of this fire-place, went round the outside 

 of the boiler, were occasionally cleaned ; b is the canal 

 by which the smoke went off into the chimney. 



The entrance into the fire-place, and the conical per- 

 foration in the wall of the fire-place which serves as a 

 window for observing the fire, are marked by dotted 

 lines. The position of the inside door of the fire-place 

 is marked by a dotted line, c, d. The circular dishing- 

 grate is seen in its place ; and the walls of the flues 

 under the boiler are all seen. The crooked arrows in the 

 flues show the direction of the flame. (See page 92.) 



PLATE IV. 



Fig. 19 is a vertical section of the boiler represented 

 in the foregoing plate (Fig. 17). This section is taken 

 through the middle of the boiler, of the fire-place, and of 

 the cover of the boiler. A is the ash-pit, with a section 

 of its register door ; B is the fire-place, and its circular 

 dishing-grate ; C is the entrance by which the fuel 

 is introduced, with sections of its two doors ; D is a 

 space left void to save bricks ; E is the boiler, and F 

 its wooden cover ; m is the steam chimney, which is 

 furnished with a damper ; R, R, is the vertical wall of 

 the house against which the brick-work in which the 

 boiler is fixed is placed ; a, b, is the curb of timber in 

 which the boiler is set. 



The manner in which the cover of the boiler is con- 



