and the Economy of Fuel. 77 



brick-work which supports the boiler, equal in diameter 

 to the circular grate, and from 6 to 10 inches high, more 

 or less according to the size of the boiler ; that the boiler 

 is set down on the top of the circular wall which forms 

 this fire-place, a small opening from 3 to 4 or 5 inches 

 in length taken horizontally, and about 2 or 3 inches 

 high, being left on one side of this wall at the top of it, 

 that the flame which burns up under the middle of the 

 bottom of the boiler may afterwards pass round (in a 

 spiral canal constructed for that purpose) under that 

 part of the bottom of the boiler which lies without the 

 top of the wall of the fire-place on which the boiler 

 reposes. The flame having made one complete turn 

 under the boiler in this spiral canal, it rises upwards, 

 and, going once round the sides of the boiler, goes off by 

 a horizontal canal, furnished with a damper, into the 

 chimney. * 



In order that the top of the circular wall of the fire- 

 place on which the boiler is seated may not cover too 

 much of the bottom of the boiler, its thickness is sud- 

 denly reduced in that part (that is to say, just where it 

 touches the boiler) to about half an inch. 



The opening by which the fuel is introduced into the 

 fire-place is a conical hole in a piece of fire-stone, which 

 hole is closed by a fit stopper made of the same kind of 

 stone. The ash-pit door and its register are finished 

 with so much nicety that, when they are quite closed, 

 the fire almost instantaneously goes out. 



The dimensions of the boiler, in which the experi- 

 ments of which I am about to give an account were 

 made, are as follows : 



Diameter J jj ek)w ' ^^ I i nc h es , English measure. 

 Depth ...... 14.52 ) 



