The Armstrong time-fuse is made of gun-metal. A ring of fuse composition similar to that of the old Bormann fuse is pressed in a channel whose outer wall is marked in inches and tenths. This fuse composition is covered by a movable collar which is kept in place by a nut. Attached to this movable collar is a small chamber containing a detonator. When the gun is fired, this detonator ignites the composition at the point at which it is set, and the flame travels around until it meets the magazine, or blowing-chamber, which communicates the flame to the shell-charge. The Pettman percussion fuse is made up of seven principal parts—the body, top plug, steady plug, detonating ball, cone plug, lead cap, and bottom plug. The top and bottom plugs are set fast; the shock of firing sets back all the other parts, crushing the lead cap over the cone and bottom plugs, which by their shape are all held fast when jammed together. The detonating ball, whose surface is covered with a detonating composition, is carried straight back and prevented from coming in contact with the sides of the chamber by the steady plug. When the projectile strikes, however, the steady plug starts forward and releases the ball, which, coming in contact with the sides of the fuse, explodes the detonating powder and the flame is carried by holes through the lower plugs to the charge. [Illustration: Pettman Percussion Fuse.] [Illustration: Laboratory Percussion Fuse.] PRIMERS. [Illustration: Electrical Primer.] [Illustration: Quill Friction Primer.] Gun-locks are no longer used in the navy. Guns are fired by means of either the friction or the electric tube. The quill friction-tube is used exclusively for the navy. This tube is of two sizes, the short and the long, the latter being used with the heavy calibres. The quill is driven with mealed powder, and a hole is pierced through the centre. The top and bottom are stopped with shellac putty. In the upper part of the tube an iron-wire friction-bar is inserted, having a sprinkling of detonating composition and mealed powder on one side. The top of the tube is strengthened by a thread woolding and a leather loop, which slip over a pin placed forward of the vent. The naval electric tube consists of a quill body and a xylonite bottom, the quill being of a diameter to slip completely into the vent. Within this quill are insulated terminals of wire connected by a platinum-silver wire bridge surrounded by priming composition. The whole tube goes into the vent, a stop on the insulating wires preventing it from going too far. [Illustration: Centre Hind-Sight—Muzzle-Loaders.] [Illustration: Wood Scale.] SIGHTS. [Illustration: Sliding Leaf Tangent Sight—Muzzle-Loaders.]