re put in.

[Illustration: RIVETING THE BOILERS.]

Sometimes operations must be performed upon the sides of the boiler
requiring the force of machinery. To effect this purpose, shafts carried
by the central engine to which we have already alluded, are attached to
the walls in various parts of the room, as seen in the engraving.
Connected with these shafts are various drilling and boring machines,
which can at any time be set in motion, or put to rest, by being thrown
in or out of gear. One of these machines is seen on the right of the
boiler above referred to, and another in the left-hand corner of the
room quite in the back-ground. Near the fore-ground, on the left, is
seen a forge, where any small mass of iron may be heated, as occasion
may require.

The semi-cylindrical piece which lies in the centre of the room, toward
the fore-ground, is part of a locomotive boiler, and is of course much
smaller in size than the others, though it is constructed in the same
manner with the large boilers used for sea-going ships. The process of
riveting, as will be seen by the engraving, is the same. One man holds
up against the under side of the plate a support for the rivet, while
two men with hammers form a head above--striking alternately upon the
iron which protrudes.

From the boiler we proceed to the cylinder, which is in fact the _heart_
of the engine,--the seat and centre of its power. It is to the cylinder
that the steam, quietly generated in the boiler, comes to exercise its
energy, by driving, alternately up and down, the ponderous piston. The
cylinder must be strong so as to resist the vast expansive force which
is exercised within it. It must be stiff, so as to preserve in all
circumstances its exact form. It must be substantial, so as to allow of
being turned and polished on its interior surface with mathematical
precision, in order that the piston in ascending and descending, may
glide smoothly up and down, without looseness, and at the same time
without friction. To answer these conditions it is necessary that it
should be formed of cast iron.

The cylinders are cast, accordingly, in the iron foundry, which, as will
be seen by the plan, is on the left, as the visitor enters the works.
There is a range of monstrous cranes extending through the interior of
the room, as represented in the plan, one of which is exhibited
conspicuously in the engraving below. At different places in the ground,
beneath this foundry,