and the Economy of Fuel. 109 



of the flues through which the flame and smoke were 

 obliged to pass to get into the chimney had been dimin- 

 ished more than half (or reduced from 70 to about 30 

 feet), the strength of the draught of the fire-place was 

 much increased, as was evident not only from the in- 

 creased violence of the combustion of the fuel, which 

 was very apparent, but also from another circumstance, 

 which I think it my duty to mention. Before the flue 

 round the boiler was closed, if too much fuel was put 

 into the fire-place at once, it not only did not burn with 

 a clear flame, but frequently the smoke, and sometimes 

 the flame, came out of the fire-place door, even when 

 the damper in the chimney was wide open ; but, after 

 this flue was closed up, it was found to be hardly pos- 

 sible to overcharge the fire-place, and the fuel always 

 burned with the utmost vivacity. 



I ought to inform my reader that, though the entrance 

 into the flue which went round the outside of the boiler 

 was closed, and another and a shorter road opened for 

 the flame and smoke to pass off into the chimney, yet 

 the cavity of the flue remained ; and, by means of open- 

 ings (c, c, c, c, c, c, Fig. 21, Plate V.) about 6 inches 

 square in the brick-work which separated this old road 

 (which was now shut up) from the flues under the boiler, 

 the flame was permitted to pass into this cavity, and to 

 spread itself round the outside of the boiler. This con- 

 trivance (which I would recommend for all boilers) not 

 only prevents the escape of the heat out of the boiler 

 by its sides, but contributes something towards heating 

 it ; and, as the openings in the sides of the flues do not 

 sensibly impede the motion of the flame, they can do 

 no harm. 



As the two experiments, the results of which I am about 



