happy to do, as I had on hand the peculiar bed for these engines, which I did not break up after the order was countermanded, but had it set up against the wall of the shop in readiness for what might happen. These two engines were both in successful operation when my own operations ceased; the remaining three engines were to be added as their business required. The engineer of that company was an original investigator. He had a battery of return-tubular boilers, each one crammed full of tubes according to the usual methods of boiler-makers. He provided himself with pieces of lath one inch wide, one eighth of an inch thick, and four inches long, and laid one in the front end of each tube in one of his boilers and left them there for twenty-four hours. He had made a diagram of his boiler on which he numbered every tube and put a corresponding number on every piece of lath. In taking them out they presented an astonishing revelation, which he showed me. Some of the pieces were burned almost to a coal and some were scarcely discolored, while the great body of them presented various effects of heat between these extremes. These showed distinctly the enormous differences in the temperature of the gases passing through the different tubes, and that fully one half of the tubes did little or no work in evaporating the water. They taught a lesson which boiler-makers, who count every additional tube they can get into a boiler as so much added heating surface and rate their boilers accordingly, have no anxiety to learn, but which I afterwards turned to good account, as will be seen. About the last and the most interesting engine that I built while in Philadelphia was one for the firm of Cheney Brothers, silk-manufacturers, of South Manchester, Conn. This was a cross-compound, the first and the last compound engine that I ever built, and it is the only engine in this country to which I applied my condenser. The cylinders were 12 and 21 inches in diameter, the stroke 24 inches, and the shaft made 180 revolutions per minute. The condenser presented a new design in one respect; the air-pump was double-acting and made only 45 double strokes per minute, being driven by a belt from the engine shaft and the motion reduced by gears 1 to 4. This engine ran perfectly from the start, and I looked forward with confidence to a demand for many more of the same type. The diagrams made by it are here reproduced. [Illustration: Scale, 1″ = 32 Lbs. Atmosphere Scale, 1″ = 16 Lbs. Atmosphere Diagrams from my First and Only Compound Engine.]