This method has the advantage of adjusting the sights in any plane parallel to the axis, as in the case of the side-sights of rifled and other cannon.
ADJUSTMENT OF THE SIDE-SIGHTS.
40. The gun having been levelled, and the trunnions placed horizontal, a centre line is to be drawn on the top of the left (or right) rimbase.
The support for the sight is then to be fitted to the breech, at the distance from this line marked on the pattern-sight for its calibre, with the bottom of the sight-notch in the bar, exactly the height of the front sight (one inch) above the upper surface of the rimbase; the sight-bar perpendicular.
It is advisable to place a very thin sheet of rubber under the support, to prevent the heads of the screws from being jumped off by the vibration. The screws have the same thread as those for the present reinforce-sight.
After the breech-sight is adjusted, a parallel to the axis of the bore is to be drawn in the usual manner, and the front sight screwed in on the rimbase.
Some trifling adjustment may then be required, to bring the height of the top of the front sight and the bottom of the sight-notch parallel to the axis of the bore in both the horizontal and vertical planes.
PRESERVATION OF GUNS.
41. Guns received at Navy Yards are to be carefully placed on the ranges of masonry, capped with iron skids or bars. It is intended that these shall be so high that the guns may be rolled upon them without their trunnions touching the ground, and that the earth will not be beaten up against their muzzles by heavy rains.
42. The surface over which guns are to be stowed should be kept firm and clear of all vegetation, and for this purpose should be covered with cinders from the smiths' forges, or other substance unfavorable to or destructive of the growth of plants and grasses.