356 Description of a new Boiler, constrticted 



its heating, we may compare the extent of surface that 

 it presents to the action of the fire with that of the flat 

 bottom of a common boiler. 



The diameter of the bottom of a cylindrical boiler 

 being 12 inches, the surface is 113.88 square inches; 

 but the surface of the sides of the seven tubes that de- 

 scend from the flat bottom of our boiler (which is like- 

 wise 12 inches in diameter) is 593.76 square inches. 

 Therefore the new boiler has a surface exposed to the 

 direct action of the fire, more than five times greater 

 than that of a boiler of equal diameter and of the ordi- 

 nary form ; how much this difference must affect the 

 celerity of heating is easy to conceive. 



In the manner in which boilers are usually set, their 

 vertical sides are but little struck by the flame, and on 

 that account I have not taken the effect of the sides into 

 consideration in my estimate ; but even taking them 

 into account, the new boiler will always have a surface 

 exposed to the fire at least twice as great as that of a 

 common cylindrical boiler of the same diameter, as can 

 easily be shown. 



The new boiler being 12 inches in diameter and 12 

 inches high, and each of its seven tubes being 3 inches 

 in diameter and 9 inches high, its surface is 1160.44 

 square inches, without reckoning the circular plate that 

 closes its top, nor its neck. 



The surface of the bottom and sides of a cylindrical 

 boiler of 12 inches in diameter and 12 inches high will 

 be 566.68 square inches. 



As the quantity of heat that enters a boiler in a given 

 time is in proportion to the extent of surface that the 

 boiler presents to the fire, it is evident that, other 

 circumstances being the same, a .boiler with tubes de- 



