The position of the piece, H, is, in effect, variable with the pressures that are manifested in the pump. It will be seen that the latter has a tubular appendage, g, in whose interior there plays what is called a "starting rod," h, which is constantly submitted to the pressures existing in the interior of the pump, and which rests against the lower arm, H¹, of the piece, H. But this latter is also loaded at the opposite side with heavy counterpoises, i, which counterbalance, within a determinate limit, the action of the rod, h, that tends constantly to cause the lever, H, to oscillate around its pivot, in the brackets, c. To sum up, then, as long as the pressure in the pump has not reached a determinate limit, the lever, H, held by its counterpoises, _i_, will keep the position shown in Fig. 16, and for which the center of oscillation, f, corresponds with the maximum stroke of the pump piston. But as soon as such limit is exceeded, the equilibrium being broken, the action of the rod, h, predominates, the piece, H, reverses from right to left, the point of oscillation, f, moves forward in the slots, d, and the stroke of the piston is reduced just so much. If, finally, the pressure continues to increase, the motion of the piece, H, will continue, and the point of oscillation, f, will reach the position for which the motion of the piston ceases completely (Fig. 18). But it results further, therefrom, that if when such position is reached, the pressure diminishes, the lever, H, will, under the influence of its counterpoise, tend to return to its first position and thus set the piston in motion. As we remarked in the beginning, the automatism of these functions is absolutely complete. It will be remarked that the piece, H, is provided with an appendage, H², whose interior forms a rack. This rack engages with a pinion, I, mounted on an axle, J, which carries externally a fly wheel, K. This axle, J, moves with the various displacements of the lever, and its fly wheel overcomes by its inertia all backward and forward shocks resulting from the thrusts due to the sliding of the steel slides in the different positions of the connecting rods. Such shocks would make themselves especially felt while the dead centers were being passed. The velocity with which this pump runs varies from 75 to 80 revolutions per minute. It easily gives a pressure of 200 atmospheres. With a hydraulic press having a piston O.27 of a meter in diameter, it permits of effecting in ten minutes the extraction of the oil from 25 kilogrammes of colza seeds. Referring to the drawings, the scales for Figures 16, 17, 18 are one-fifteenth actual size, and Figures 19, 20, 21, one-tenth.--_Machines, Outils et Appareils_. * * * * * IMPROVED DREDGER.