t; it is made to fit closely over it. On each side
there is a small tube; a thread is cut in one, through which a fine
screw, held by a stud on the permanent part of the handle, works and
gives it motion; a guide runs through the other. Seen through the slit
is a small plate of silver inserted in the staff, and a fine mark upon
it to show the place of zero, when the points are adjusted. The
zero-mark on the scale is made to correspond with it by means of the
screw just mentioned.

The points are of steel, with a strong shoulder at one end, below
which the screw is cut that fits into the socket in the head. A wrench
is made to fit the other end, so as to turn the point firmly into its
place. They are made of such a length that they will just pass into
the adjusting-ring when they are all in place. To this instrument
belong the adjusting-rings and the muzzle-rest in the form of T; of
the rings there is one for each calibre, reamed out to the exact
minimum diameter of the bore. The latter can be used for any class of
guns. Its office is to keep the staff of the star-gauge in the axis of
the bore. For this purpose it contains a groove, above the
perpendicular branch, to receive the lower half of the staff. There is
a movable slide on each branch, which can be adjusted to marks for
each calibre, so that points projecting from their rear will enter the
muzzle and hold the rest in place. In this position the upper edge of
the transverse branch coincides with the diameter of the bore.

A hook is pivoted on the inner side of the transverse branch, on one
side of the groove, and so fitted that when the star-gauge is in the
gun, it embraces one-half of that portion of the staff which is above
the groove. Therefore, if the transverse branch be placed so as to
coincide with the axis of the trunnions, the hook thrown over the
staff, and the latter turned so that the centre line just meets the
end of the hook, the perpendicular points will be perpendicular to the
axis of the trunnions. If the staff is then drawn out carefully, the
measurements will all be taken in the same plane. A notch in the end
of the hook, made to coincide with the plane of the muzzle, may be
used for marking the distances on the staff.

The upright branch is movable, and is made to fit into the end of the
transverse branch, for convenience and security in packing.

In examining the bores after proof, it has been found that the
greatest indentation occurs in