The main difference between this carriage and the others is the use of a hydraulic recoil cylinder working in a manner quite different from the English style. The cylinder itself is of steel, and is hung on trunnions _to the carriage_. The piston-rod runs completely through it, and is secured at each end of the slide. Both ends of the cylinder are closed by cast-iron heads with stuffing-glands. The forward head, being the one which receives the violence of the recoil, is secured by a heavy iron brace which fastens to the cylinder trunnions. The cylinder is filled with glycerine, the filling and drip holes being both at the rear end. It rests and slides on a bed fixed along the middle of the slide. The arrangement for checking recoil, and also for governing violent movements of the carriage, is contained in the piston-head. This head is made up of two discs which are bolted together, the interior face of each being hollowed out so as to form a chamber in the piston-head. Four holes are bored through each disc into the chamber, but they are not in line, the hole in one disc coming opposite a blank in the other. Four small valves close the inner ends of the forward holes, and these valves are secured to a plate which is free to move back and forth in the little chamber, and thus open or close the holes. A rod from the back of this plate passes through the hollow rear end of the piston-rod, and seats against a carriage-spring on the rear transom of the slide. This spring holds the valves forward, closing the forward piston-holes. A small hand-lever on the valve-rod enables it to be drawn back, thus opening the valves at will. The action of the compressor is as follows: The recoil of the gun carries the cylinder to the rear and violently contracts the space forward of the piston-head; the oil is forced with violence through the forward holes, pressing back the small valves and escaping by the other holes to the rear of the cylinder. As the recoil ceases, the force of the spring carries the valve-stem and its valves forward again, closing the holes. The gun is held thus in position, as it cannot run out unless the valves permit the oil to pass into the forward end of the cylinder again. The pressure, however, comes against the back of the valves and keeps them closed. A slight turn of the hand-lever opens the valves, and the oil gaining free passage permits the gun to run out. The moment that the gun starts, however, to run out violently, a single movement closes the valves and the gun is held fast. [Illustration: Piston-Head.] [Illustration: Rear End of Piston-Rod and Connections.] _Slide-Carriage for the Short 24-cm. Gun, Pattern 1876._