A little incident in connection with this work, which made a deep impression on my mind, and has since afforded me some food for reflection, seems worth relating. The printing was done in London, and I did not see the proof, so I had to take especial pains with the copy, having no opportunity to revise it. I was living in Harlem, and at one time having no suitable envelope for mailing, and none being obtainable there, I took a Third Avenue horse-car for an eight-mile ride down to the New York post office, intending to get some envelopes at a stationery store on Beekman Street, and mail the portion of the copy which I then had ready at the general post office. I had hardly taken my seat when Mr. Allen got into the car. He was living in Mott Haven, and I had not seen him for a long time. Besides ourselves the car was nearly if not quite empty. He came and sat down by me, and I opened my copy and read to him something in which I knew he would be interested. He said to me, in his gentle way, “You would not express it exactly that way, would you?” On the instant it flashed on my mind that I had made a stupid blunder, and I replied, “I guess I wouldn’t,” and, thanking him for calling my attention to it, I left the car, and returned home and corrected it. I have quite forgotten what the point was, and if I remembered it, I would not tell. But I have often asked myself who sent Mr. Allen there, saving me from publishing a mortifying blunder. I expect some sweet spirit will tell me before long. [Illustration: The Prototype of the Modern High-speed Engine, Fly-wheel Side.] [Illustration: The Prototype of the Modern High-speed Engine, Crank Side.] As soon as this book was off my hands, I devoted myself to the revision and standardizing of the engine. As made up to that time, it was not reversible, and the valves could not be handled. It could not therefore be used in rolling-mills, the field to which I felt already that it was especially adapted. Moreover, every engine should be capable of being backed in starting, as otherwise whenever it had stopped with the piston at a point later than the latest point of cut-off, or say in the last half of the stroke, which it would do half the time, it would need to be pulled around by hand to a position in which one of the admission ports would be open. This in a large engine, or one connected with extensive lines of shafting, would be a serious matter, so much so that in some engines little starting cylinders are required. [Illustration: Longitudinal Section of Cylinder and Valves.] [Illustration: Cross-section of Cylinder and Valves.] [Illustration: Elevation and Plan of Valve Connections.] I had also determined to use the equilibrium admission valves with adjustable pressure plates, according to the drawings sent to me by Mr. Allen in 1863, and to abandon the separate steam chest, and put the exhaust valves on the opposite side of the cylinder.