which rotate with great
rapidity,--usually, about four hundred times in a minute. These stones
are covered with large, movable wooden cases, to keep the water from
flying about the room, or over the workmen.

An iron rod is inserted into the bore of the barrel, and is fitted very
closely. The rod is furnished with a handle, which is used by the
workman for holding the barrel against the stone, and for turning it
continually while he is grinding it, and thus bringing the action of the
stone upon every part, and so finishing the work in a true cylindrical
form. In the act of grinding, the workman inserts the barrel into a
small hole in the case in front of the stone, and then presses it hard
against the surface of the stone by means of an iron lever which is
behind him, and which he moves by the pressure of his back. The work is
very rapidly and smoothly done.

There are twelve sets of stones in the grinding-room in constant
operation day and night. These stones, when set up, are about eight feet
in diameter, and are used to within twelve inches of the centre. They
last about ten days.

The operation of grinding was formerly regarded as a very dangerous one,
from the liability of the stones to burst in consequence of their
enormous weight and the velocity with which they revolve; but, about
twenty years since, a new method of clamping the stone was adopted, by
means of which the danger of bursting is much diminished. The last
explosion which took place in this department occurred about nine years
ago. The operation of grinding, however, is objectionable also from the
very unhealthy nature of the work. Immense quantities of fine dust fill
the air, and the premises are always drenched with water, making the
atmosphere damp and unwholesome.

In former times, it was customary to grind bayonets as well as barrels;
but the former are now milled instead, thus making an important saving
in expense, as well as gain in the health of the establishment. No mode,
however, has yet been devised for dispensing with the operation of
grinding the barrel; but the injury to the health, in this case, is much
less than in the other.

When the barrels are nearly finished, they are proved by an actual test
with powder and ball. To this purpose a building at the water-shops,
called the proving-house, is specially devoted. It is very strongly
built, being wholly constructed of timber, in order to enable it to
resist the force of the explosi