While they were still lying on the floor of the shop ready for shipment, I had an opportunity of submitting them to the criticism of William R. Jones, the manager of the Edgar Thompson Steel Works, to whom, as already related, I had sold a small engine and governors for his large ones. I had not made these engines properly in one respect, as he pointed out to me that, for rolling-mill uses, they must be made capable of being run backwards by hand from any position, a requirement of which I had been ignorant. I soon made the necessary additions to the valve-gear which enabled this to be done. I never knew how Mr. Jones came to make this opportune visit, but undoubtedly Mr. Holley sent him. I had another visitor before these engines were shipped. It was the manager of the Laclede rolling mill at St. Louis, accompanied by his engineer. They had designed a system of driving several trains of rolls from one engine, the power of which was to be transmitted through gearing. They were greatly fascinated by the appearance of the engines, and gave me an order for a large engine on the spot. This engine afforded me a curious experience. When it was started, teeth were broken out of the gear at the very first revolution, and I received a telegram from them telling me of this misfortune and that I must come to St. Louis immediately and see what was the trouble with _the engine_. I was too busy to go myself, but Mr. Phillips kindly permitted his engineer, Mr. Collins, to go in my place. Mr. Collins took with him everything necessary to expose the defect, whatever it might be, which we expected would be found in the gearing. Among other things he had the pattern-maker prepare for him two or three short pieces of lath about two inches wide and one eighth of an inch thick; these latter proved to be all that he needed. On his arrival the proprietors assured him there could be no fault with the gearing, for they had it made by the most eminent engineering firm in St. Louis. The members of this firm showed him triumphantly the broken pieces and directed his attention to the perfect soundness of the metal, as proved by the fractured surfaces. His first experiment was to whittle an end of one piece of lath to fit exactly between two teeth of a wheel at one end of the space. To his amazement he found that this templet would not fit in any other space around the whole wheel, every one was in some degree or other too large or too small; neither would the templet fit in the opposite end of the same space. This one experiment settled the matter; the engine, to be sure, had broken the gears, because the larger teeth of the driving-wheels had wedged into the smaller spaces of the driven wheels. How such work could be produced was a puzzle to Mr. Collins; as for myself, I have never wondered at any imperfection in gearing since my experience with Mr. Whitworth’s work. The owners of the rolling mill applied for advice to Samuel T. Wellman, the