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exists among the documents left by the inventor a contract signed by Demeuldre, at Brussels in 1845, from which it appears that he undertook to obtain a patent of importation into Prussia for the new valve motion, subject to an assignment by Walschaert of half of the profits to be deducted from the introduction of the new valve motion in that country. It is probable, however, that this contract was never carried out.
The design attached to the Belgian patent is reproduced in Fig. 26. In this primitive arrangement the link oscillated on a fixed shaft, in regard to which it was symmetrical, but it had an enlarged opening at the centre so that only at the ends was it operated without play by the link-block, which was made in the form of a simple pin. There was only one eccentric, the rod of which terminated in a short T carrying two pins. The reverse shaft operated the eccentric rod and maintained it at the desired height. For one direction the lower pin of the T engaged in the lower end of the link, and to reverse the engine the rod was raised so that the upper pin engaged in the upper end of the link. The angle of oscillation of the link varied with the position of the pin in the link, and this oscillation was transmitted by an arm to the combination lever, which was also operated by the crosshead.
The central part of the link could not be used for the steam distribution, as it was necessary to enlarge it to allow for the play of the pin which was not in operation. It may be asked why the inventor used two separate pins mounted on a crosspiece on the end of the eccentric rod instead of a single pin on the centre of the rod which would have served for both forward and backward motion without requiring the centre enlargement of the link. It must be borne in mind that the raising or lowering of the eccentric rod by the reverse shaft was equivalent to a slight change in the angular advance of the eccentric. Consequently, with a link of sufficient length, to keep down the effect of the angularity it was necessary to reduce as much as possible the movement of the eccentric rod. Notwithstanding its differences the mechanism described in the patent of 1844 is in principle similar to the valve motion with which every one is to-day familiar, and which the inventor constructed as early as 1848, as is shown by a drawing taken from the records of the Brussels shops, on which appears the inscription "variable expansion; E. Walschaerts' system applied to Locomotive No. 98, Brussels, September 2d, 1848.”
Fig. 27, taken from this drawing, shows the valve motion as we know it to-day. For although it is true that the link and the combination lever are usually placed in a different position so as to shorten the
eccentric rod and the valve-stem, yet the design of the locomotive often requires an arrangement similar to that shown above. The system which Mr. Heusinger Von Waldegg invented in 1849, and which he applied in 1850 to 1851, differs only in a few insignificant particulars from that shown in Fig. 27. Walschaerts had therefore preceded him.