EARLY REVERSING MOTIONS.
In the engineering practice of the world, before the locomotive and marine engines came into use, there was no need for devices to make engines rotate in more than one direction. When the need for a reversible engine first arose, it was met by very crude appliances. Locomotives were kept at work, earning money for their owners, which were reversed by the man in charge stopping the engine, and by means of a wrench changing the position of the eccentric by hand. A decided improvement on the wrench was the movable eccentric, which was held in forward or back gear by stops; the operation of reversing being done by a treadle or other attachment located near the engineer’s position. A serious objection to this form of reversing gear was, that the abrasion of work enlarged the slot ends, and wore out the stops, leading to inaccuracy and frequent breakage. A somewhat better form of reversing motion was a fixed eccentric, with the means at the end of the eccentric-rod for engaging with the top or bottom of a rocker-shaft, which operated the valve-stem. This was the form of reversing motion used on the early Baldwin engines. Numerous other appliances, more or less defective, were experimented with before the double fixed eccentrics were introduced. Till the link was applied to valve-motion, the double eccentrics—an American invention—were the most important improvement that had been made on the locomotive valve-motion since the incipiency of the engine. The V hook, in connection with the double eccentrics, made a fair reversing motion in comparison to any thing that had preceded it. The objection to the hook was, that, when the necessity arose for reversing the engine while in motion, much difficulty was experienced in getting the hook to catch the pin. As a simple, prompt, and certain reversing motion, the link was readily acknowledged to be far superior to any thing that had previously been tried.