Steam Engine, 35^ 
first smaller cylinders, goes under the third, over the 
fourth, under the fifth, over the sixth, under the se- 
venth, and partly over partly under the eighth small 
cylindric tube. The direction of the flame, till it reach- 
es the last- mentioned tube, is shown by the dotted ciirv- 
ed line and arrows. When it has reached that end 
of the furnace it is carried by the flue C to the other 
side of a wall, built under and in the direction of the main 
cylinder A, and then returns under the seventh smaller 
cylinder, over the sixth, under tire fifth, over the fourth, 
under the third, over the second, and partly over partly 
under the first ; when it passes into the chimney. The 
wall before mentioned, which divides the furnace longi- 
tudinally, answers the double purpose of lengthening the 
course which the flame and heated air ha\ e to traverse, 
giving off heat to the boiler in their passage, and of secur- 
ing from being destroyed by the fire the flanges or other 
joinings employed to unite the smaller tubes to the main 
cylinder. The ends of the smaller cylindric tubes rest on 
the brick- work which forms the sides of the furnace, and 
one end of each of them is furnished with a cover, secur- 
ed in its place by screws or any other adequate means, 
but which can be taken oft' at pleasure, to allow the tubes 
to be freed, from time to time, from any incrustation or 
sediment which may be deposited in them. To any con- 
venient part of the main cylinder A, a tube is affixed, to 
tonvey the steam to the steam-engine, or to any vessel 
intended to be heated by means of steam. 
When very high temperatures are not to be employed, 
the kind of boiler just described is found to answer very 
well ; but. where the utmost force of the fire is desirable, 
Mr. Woolf, for a reason which shall be afterwards men- 
tioned, combines the parts in a manner somewhat differ- 
ent, though the same in principle. Having been permit- 
ted to inspect two boilers of tills kind Which he is now 
