It is here shown as mounted on a torpedo launch and ready for action.  The shell or projectile is fired by compressed air, admitted from an air reservoir underneath by a simple pressure of the gunner’s finger over the valve.  The air passes up through the center of the base, the pipe connecting with one of the hollow trunnions.  The valve is a continuation of the breech of the gun.  The smaller cuts illustrate Lieutenant Zalinski’s plan for mounting the gun on each side of the launch, by which plan the gun after being charged may have the breech containing the dynamite depressed, and protected from shots of the enemy by its complete immersion alongside the launch; and, if necessary, may be discharged from this protected position.  The gun is a seamless brass tube of about forty feet in length, manipulated by the artillerist in the manner of an ordinary cannon.  Its noiseless discharge sends the missile with great force, conveying the powerful explosive within it, which is itself discharged internally upon contact with the deck of a vessel or other object upon which it strikes, through the explosion of a percussion fuse in the point of the projectile.  A great degree of accuracy has been obtained by the peculiar form of the projectile.

[Illustration:  Pneumatic dynamite gun torpedo vessel.]

The projectile consists of a thin metal tube, into which the charge is inserted, and a wooden sabot which closes it at the rear and flares out until its diameter equals that of the bore of the gun.  The forward end of the tube is pointed with some soft material, in which is embedded the firing pin, a conical cap closing the end.  A cushion of air is interposed at the rear end of the dynamite charge, to lessen the shock of the discharge and prevent explosion, until the impact of the projectile forces the firing pin in upon the dynamite and explodes it.  Many charges have been successfully fired at Fort Hamilton, N.Y.  As the center of gravity is forward of the center of figure in the projectile, a side wind acting upon the lighter rear part would tend to turn the head into the wind and thus keep it in the line of its trajectory.  A range of 11/4 miles has been attained with the two inch gun, with a pressure of 420 lb. to the square inch, and one of three miles is hoped for with the larger gun and a pressure of 2,000 lb.

* * * * *

ROPE PULLEY FRICTION BRAKE.

A novel device in connection with rope pulley blocks is illustrated in the annexed engravings, the object of the appliance being to render it possible to leave a weight suspended from a block without making the tail of the rope fast to some neighboring object.  By this arrangement the danger of the rope slipping loose is avoided, and absolute security is attained, without the necessity of lowering the weight to the ground.  The device itself is a friction brake,