62 Of the Management of Fire 



it be necessary that its particles individually be brought 

 into actual contact with that body, it is evident that the 

 form of a boiler, and of its fire-place, must be matters 

 of much importance ; and that that form must be most 

 advantageous which is best calculated to produce an 

 internal motion in the flame, and to bring alternately 

 as many of its particles as possible into contact with the 

 body which is to be heated by it. The boiler must not 

 only have as large a surface as possible, but it must be 

 of such a form as to cause the flame which embraces it 

 to impinge against it with force, to break against it, and 

 to play over its surface in eddies and whirlpools. 



It is therefore against the bottom of a boiler, and not 

 against its sides, that .the principal efforts of the flame 

 must be directed ; for when the flame, or hot vapour, 

 is permitted to rise freely by the vertical sides of a 

 boiler, it slides over its surface very rapidly, and, there 

 being no obstacle in the way to break the flame into 

 eddies and whirlpools, it glides quietly on like a stream 

 of water in a smooth canal ; and the same hot par- 

 ticles of this vapour which happen to be in immediate 

 contact with the sides of the boiler at its bottom or 

 lower extremity, being continually pressed against the 

 surface of the boiler as they are forced upwards by the 

 rising current, prevent other hot particles from approach- 

 ing the boiler ; so that by far the greatest part of the heat 

 in the flame and hot vapour which rise from the fire, 

 instead of entering the boiler, goes off into the atmos- 

 phere by the chimney, and is totally lost. 



The amount of this loss of heat, arising from the 

 faulty construction of boilers and their fire-places, may 

 be estimated from the results of the experiments re- 

 corded in the following chapter. 



