Steam Engine. 35S 
about a hundred and fifty pounds, and the boiler twenty- 
two pounds. 
In order to form an estimate of the advantage which 
the particular form of this boiler gives it in accelerating 
its heating, we may compare the extent of surface that it 
presents to the action of the fire, with that of the flat bot- 
tom of a common boiler. 
The diameter of the bottom of a cylindrical boiler being 
twelve inches, the surface is 113.88 square inches ; but 
the surface of the sides of the seven tubes that descend 
from the flat bottom of our boiler (which is likewise twelve 
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 boil- 
er of equal diameter, and of the ordinary 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 con- 
sideration in my estimate ; but even taking them into ac- 
count, the new boiler will always have a surface exposed 
to the fire, at least twice as great as that of a common cy- 
lindrical boiler of the same diameter, as can easily be 
shewn. 
The new boiler being twelve inches in diameter, and 
twelve inches high, and each of its seven tubes being three 
inches in diameter, and nine 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 twelve inches in diameter, and twelve 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 ejctent of surface that the 
