America was eminently the land of the cut-off system, an early application of which was on steamboats. The earliest device for this purpose was the elegant Stevens cut-off, which still keeps its position on the class of boats to which it was first applied, though commonly modified by the Sickles improvement. In this system the exhaust and the admission valves are operated by separate eccentrics on opposite sides of the engine, and all the valves have the amount and rapidity of their opening and closing movements increased by the intervention of wiper cams, those for the admission valves being very long and giving a correspondingly greater enlargement of opening. The valves were double poppet valves, moving nearly in equilibrium in directions vertical to their seats. This cut-off was found to be capable of improvement in one important respect. The closing motion of the valve grew slower as the valve approached its seat, and while the piston was moving most rapidly much steam passed through the ports at a lower pressure, and so a great part of its expansive value was lost. This was technically termed “wire-drawing.” To remedy this defect Mr. Sickels invented his celebrated trip cut-off. The valve, lifted by the Stevens wiper, was liberated by tripping the mechanism, and fell quickly to its seat, which it was prevented from striking forcibly, being caught by water in a dash-pot. The steam was thus cut off sharply and the economy was much improved. The pressure used in this system was only about 25 pounds, the vacuum being relied upon for the larger portion of the power. On the Great Lakes a pressure of 60 pounds was commonly employed, and the valves were the four cylindrical rotating slide valves afterwards adopted by Mr. Corliss. What was called the cut-off was made by a separate valve located in the steam-pipe somewhere between the engine and the boiler. On the Mississippi and its tributaries, much higher pressures were carried, condensers were not used, and the admission and release of the steam were generally effected by four single poppet valves, lifted by cams against the pressure of the steam.