144 Common Fires. [Book IL 



fo forming a conical flame like that of a common 

 candle, was it not that this effect is prevented by a 

 tube of glafs, with which he furrounds the flame, 

 which, when warmed, counteracts the attraction, which 

 the different fides of the circular flame would have 

 for each other, and fo preferves the current of air 

 free and without interruption. 



The fame principles will apply to the conftrudtion 

 of common fires. The great object mould be, to ex- 

 pofe as large a furface of the fuel as pofilble to the 

 air, or rather, if poffible, to introduce a ftrong and 

 difTufed current of air through the fire. On this prin- 

 ciple the air furnace is conftructed. It is well known 

 that thefe furnaces confift of an aperture or afh-hole 

 under the fire, and a high vent, funnel, or chimney 

 above, and that the door, by which the fuel is intro- 

 duced, is kept clofed, unlefs it Ihould be occafionally 

 opened for the purpofe of diminifhing the heat. By 

 means, therefore, of the high vent or funnel, the air 

 above is rarefied and rendered lighter, and confe- 

 quently the air below prefTes in through the am pit j 

 and if the bottom of the grate is kept clear, a ftrong 

 current of air circulates directly through the fire, and 

 fupplies it conftantly with this neceffary ingredient. 

 On fimilar principles die regifter ftoves are conftruct- 

 cd. In thefe the vent or chimney coming very near 

 the grate, the air below it is forced through the fuel, 

 and by enlarging or contracting the vent, the current 

 of air is increafed or diminifhed. The bath and pan- 

 theon ftoves -are alfo found to produce more heat in 

 proportion to the quantity of fuel than common open 

 grates, becaufe they are ufually fet high, and the afh- 

 pit or aperture below being clofed on three fides, a 

 confiderable part of the air which enters it is forced 

 up through the fire. The fame reafons will alfo fatis- 

 factorily account for the effects of a common bellows, 



winch 



