the fuel; in its rear side are fire doors, inserted for firing.
The internal arrangements of the boiler are composed of a large number of
tubes, lying across in a horizontal position, put together in sections with
return bends resembling the coils for heating buildings. These coils are of
small pipe (say one inch in diameter), and as numerous as may be necessary.
They give the required amount of steam. They are secured to wrought-iron
plates at each end by rivets. These plates lie close to the box, and are
secured to it, top and bottom. These tubes are wrought iron, firmly screwed
into the bends, so as to prevent any possible breaking.

The box has a hole through both sheets, in the same manner as a hollow
stay-bolt, through which the coil pipe passes, having no connection with
the box. After passing into the box it divides into two pipes, then
subdivides into four, and so on, until its numbers equal the number of
coils in the box, and to which each limb is attached. The upper ends of
these coils are the same in number, and are carried through at the top or
nearly the top of the box. They then run down outside to the steam chamber,
or rather water space, as the box is both steam chamber and water space.
These pipes empty their contents into the box, steam and water, as it may
come, all together. It will be observed that these coils of tube are
sufficiently separated to allow the fire to pass between them freely, and
cover their whole surface.

The mode of operation of this boiler is this: The fire box is filled 2/3
full of water. The coils are dry at starting; the space for fuel being
filled with good wood, the fire is lighted, and in a few moments the
engineer moves his hand pump, which takes its water from the box to which
it is attached, and forces it through the coils. By this means steam is
generated in from 3 to 5 minutes, so as to start the engine.

It will be seen that the water performs a complete circuit; it is taken
from the box and passed through the coils; what is steam remains in the
steam chamber, and what is not (if any) drops back into the box from where
it started. Hence it will be seen that a large surface is exposed to a
small quantity of water, and in a way that it is entirely controllable. All
the engineer has to do to surcharge his steam, is to reduce the speed of
the pump (which is independent of the main engine). By raising the heat and
quantity of water, any degree of elasticity can be given t