y for action.

When the forward and after slides are of different lengths, and the
traversing circles of different diameters, the longest slide will be
fitted with an additional rear pivot-hole and plate, to correspond
with the smaller circle, in order that the gun may be worked from the
midship pivot-bolt and shifted to the different fighting centres or
pivot-bolts of the smaller circle.

Thus, when only one pivot-gun is mounted forward and one aft, and when
they can both be brought to bear from only one end of the vessel, the
force may be doubled at that extremity by pivoting one gun on each bow
or quarter, as the case may be.

For heavy guns this is practicable in smooth water only.

Arrangements are made for shifting the broadside-guns both to the bow
and stern, in aid of the pivot-guns, when the distance of the enemy is
not too great. When the stern gun is pivoted over the rudder, one of
the broadside-guns may be worked on each side of it, in firing right
aft. Guns mounted on pivot-carriages may be fought upon the rear
pivot, on the common or shifting centre, and fired from any point of
the traversing or shifting circle, if the elevation be such as will
not endanger the decks. In this case the training must be done with
the gun run in over the rear pivot, as after it is run out the
training will be difficult, and the helm must be relied on to bring
the gun on with the object.

Guns should never be transported about the deck of a ship when
loaded.

NOTES UPON THE MANUAL EXERCISE.

FOURTH COMMAND.

"SERVE VENT AND SPONGE!"

_"The Gun Captain-serves, then stops the vent!"_

256. A difference of opinion being entertained among artillerists with
regard to the utility of stopping the vent, the continuance of the
practice, as directed in the text, is recommended.

The thumbstall has been made of various materials, but its use is
somewhat inconvenient for the Gun Captain, and he cannot feel that the
vent is stopped. At the Experimental Battery of the Ordnance Yard the
naked thumb is used, and experience shows that the gun is never so hot
as to occasion the least inconvenience, except with howitzers.

257. It has been the uniform practice at the Experimental Battery at
the Ordnance Yard, Washington, and also on board the Gunnery Ship
_Plymouth_, in 1857-'58, to use a moist sponge; and as no accident
from premature explosion has taken place in either case, the inference
is that the method is a safe one, and