However, the arc graduations are not very legible and it has been supplanted by a graduated range drum having more legible readings. The black part of the arc bears a rack which meshes with a pinion, which in turn rotates around an axle fixed on the cradle. When the cradle moves, the pinion rotates and carries with it the range drum. The elevation on level ground varies from a minus 11 degrees to a plus 20 degrees. Greater elevation may be obtained by sinking the spade. =The Recoil and Counter-recoil mechanisms= are of the Hydro-pneumatic type. Their accurate description is a secret. The following brief description will give only a general idea of the working of the mechanism. The whole apparatus is inside of the cradle through which are bored two cylinders: an upper cylinder 40 mm diameter, and a lower cylinder 66 mm diameter. These cylinders may communicate through a large hole. A piston moves in the upper cylinder, the piston rod, 24 mm diameter, being fast to the gun. In the lower cylinder are: (1) The valve carrier pipe screwed in the rear part of the cylinder supporting =spring valves=; in the inner walls of the pipe are cut two grooves; the valve carrier pipe is ended by a circular ring. (2) =The diaphragm= with its hollow rod. (3) =The loose piston= with its small rod, which may come in contact with the upper rack of the gauge. The two cylinders are full of liquid, usually Russian oil. The front part of the upper cylinder in front of the piston may communicate freely with the air through the Front Plug. The front part of the lower cylinder is closed by a plug and contains compressed air at a pressure of 150 kg. per sq. cm. =Operation.= In recoil the piston of the upper cylinder compresses the liquid, which has to pass through the spring valves and between the circular ring and the hollow rod of the diaphragm. The passage of the liquid through these different openings constitutes the braking effect. In so moving the liquid opens the valves, which are widely opened at the beginning of the recoil and gradually close in proportion to the decrease of the speed of the recoil. At the same time, the air of the recuperator is compressed by the action of the liquid on the diaphragm. When the recoil is finished, the compressed air pushes back the diaphragm. The liquid thus compressed acts on the small cylinder piston and obliges it to come back into its initial position, bringing with it the tube. The liquid in flowing back completely closes the valves and must pass between the diaphragm rod and the inner wall of the pipe. At beginning of the return into battery, the space between the rod and the bottom of the groove is large. This space decreases in proportion to the progress of the return. The passing of the liquid through this constantly decreasing space causes the braking which at the end reduces the speed of the return to nil. CARE AND PRESERVATION OF FRENCH 75. Dismountings.