and the Economy of Fuel. 93 



The top of the boiler is surrounded by a strong curb 

 (a, b, Fig. 1 7) of oak timber, to which it is attached by 

 strong copper nails, and over the boiler is built a roof, 

 or standing cover (see Fig. 1 7), similar in all respects to 

 that already described. The bottom of the boiler is flat, 

 and reposes horizontally on the top of the thin brick 

 walls by which the fire-place is divided into flues. (See 

 Fig. 1 8.) These flues do not run in the direction of the 

 length of the boiler, but from one side of it to the other ; 

 consequently the door of the fire-place is in the middle 

 of one side of the boiler. 



The sheets of copper, of which the bottom of the 

 boiler was constructed, run in the direction of the flues ; 

 and they are just so wide that their seams or joinings 

 (where they are united to each other by their sides) re- 

 pose on the walls of the flues, except only in the middle 

 flue, which, being about twice as wide as the others, one 

 seam was necessarily left unsupported, at least a consid- 

 erable part of its length. The sheets of copper used in 

 constructing this part of the bottom of the boiler are 

 rather thicker and stronger than the rest : they are just 

 0.118 of an English inch in thickness. 



The fire is made under this boiler in the middle flue, 

 which, as I have just observed, is a little more than twice 

 as wide as one of the other flues. There are five flues 

 under the boiler, namely, one in the middle 44 inches 

 wide, above in the clear (which constitutes the fire- 

 place), and two on each .side of it, in which the flame 

 circulates; one 20 inches wide, and the other 19 inches 

 wide. 



The side flues are each 14! inches deep; but as the 

 walls which separate them are much thicker below than 

 above, where the bottom of the boiler reposes on them, 



