and the Economy of Fuel. 27 



by a stone-cutter, but they cost me i florin and 30 

 kreutzers, or about is. gd. sterling each. 



Though those made of stone answered perfectly well, 

 yet I found them not better than those made of earthen 

 ware ; and as these last are much cheaper, and I believe 

 equally durable, they ought certainly to be preferred. 

 That the stopper may be made to fit with accuracy the 

 hole it is intended to close (which is necessary, as will be 

 seen hereafter), they may be ground together with fine 

 sand moistened with water. 



Sensible from the beginning of the great importance 

 of being absolutely master of the air which is admitted 

 into the fire-place to feed the fire, so as to be able to 

 admit more or less at pleasure, or to exclude it entirely, 

 I took care, in all my fire-places, to close very exactly the 

 passage into the ash-pit by a door carefully fitted to 

 its frame, the air being admitted through a semicircular 

 opening furnished with a register in the middle of this 

 door. This contrivance (which admits of no further 

 improvement) is indispensably necessary in all well-con- 

 structed fire-places, great or small. (See the Figures 

 from Fig. 9 to Fig. 16, Plate II.) 



Having occasion, in the course of my arrangements, 

 to make use of a great number of boilers, and often of 

 several boilers of the same dimensions, I availed myself 

 of that circumstance to determine, by actual experi- 

 ments, the best form for boilers, or that form which, 

 with any given capacity, shall be best adapted for saving 

 fuel. 



Two or more boilers of the same capacity, but of dif- 

 ferent forms, constructed of sheet-copper of the same 

 thickness, were placed in closed fire-places, constructed 

 as nearly as possible upon the same principles, and were 



