"Sir,--The engine has been worked. The result is ten strokes per minute, 6-feet stroke, with half a bushel of coal per hour, lifting six thousand pounds weight. This was done with water in the cistern round the condenser, which water came up to 180 degrees of heat, and remained so. The water sides of the condenser covered with this hot water was 50 surface feet. I tried it to work with the cold air sides, but I found that the cold air sides of 120 feet would only work it four strokes per minute. I should have worked the steam much higher than 50 lbs. to the inch, but being an old boiler I thought it a risk. I am now placing an old boiler of 350 feet of cold sides more to the condenser, to give a fair trial to condensing with cold sides alone. The steam below the piston was about 6 or 7 lbs. to the inch above the atmosphere. The force-pump to the boiler was about one-fifth part of the content of the cylinder, and the valve close to the boiler lifted when the force-piston was down about two-thirds of its stroke, at which time the returned steam entered the boiler again. I have no doubt of doing near ten times the duty that is now done on board ships, without using salt water in the boiler, as at present. Our boiler has been working three days and the water has not sunk 1 inch per day. I am quite satisfied the trial will be a great success. "Mr. Praed and Sir John St. Aubyn are anxious to get a high bank carried out from Chapel Angel to 15 feet below low-water mark on the bar, to make Hayle a floating harbour. "I have proposed to make a sand-lifting engine. When I built that engine for deepening Woolwich Harbour, we lifted 300 tons per hour through 36 feet of water, and 20 feet above water, 56 feet above the bottom. This was done with two bushels of coal per hour, therefore it will not cost above one penny per square fathom to lift the sand over this embankment. It is intended to get down Mr. Telford to give his opinion on it. Your remarks on it would be of service. "I remain, Sir, "Your humble servant, "RICHARD TREVITHICK." The writer having worked at these experiments, knows that their object was to employ high-pressure steam in the boiler, using it very expansively in the cylinder, and by cold surface sides reducing its bulk either to low-pressure steam or boiling water, and then force it again into the boiler. "MR. GILBERT, "HAYLE FOUNDRY, _November 14th, 1829_.