Page:The Kinematics of Machinery.djvu/429

 MURDOCHS EOTAE Y ENGINE. 407

in which moreover he does not mention the latter as the inventor of the machine.* The collection appears to have been founded about 1630.

I must here remark that the two external spur-wheels, a and b, are omitted both in Leupold's beautiful copper-plates and in the small woodcuts of Schwenter, as well as by Bramah and Leclerc. There is certainly no absolute necessity for their employment, for the pump-wheels may be used instead ; but the oblique action of the latter when in, the relative positions shown in Fig. 1 would soon damage the teeth. The use of the wheels a and b is therefore always to be recommended, and their existence will be assumed in the remaining chamber- wheel trains shown in our plate. We need not here enter into the delineation of the profiles of the wheel- teeth, which have been already mentioned in 31. We may merely mention that in this case the points of the teeth are semi-circular (as in Leupold's engraving), and the profiles of their flanks are such as work with these curves, they differ little from circular arcs.

The Pappenheim machine may be used for gaseous bodies as well as for liquids for a blower, for example, or a gas-pump. Its action also may be reversed, so that the fluid drives the machine instead of being driven by it. The machine thus becomes a prime mover, a chamber-wheel turbine, if water be the fluid used, or a rotary steam-engine if it be steam. Murdock, a contemporary of Watt,-f- attempted to apply it for the last-named purpose, using teeth with broader points, so that they could work against the chamber-walls, and fitting them also with packing pieces. The machine thus arranged could only be adapted for very light work, for the closure at the line of contact of the teeth, m n, would not suffice if a high pressure were used ; Murdock's chamber- wheel steam-engine has therefore never found its way into practical use.J


 * Ewbank, Hydraulic and other Machines, Ed. of 1870, p. 285.

t Murdock was for many years an assistant of Watt, and became eventually (practically) a partner in the firm of Boulton and "Watt. His engine, made in 1799, is described in Farcy's Treatise on the Steam Engine, p. 676, and else- where.

J So far as regards economy in the quantity of steam used Dudgeon's rotary engine, which has been a good deal advertised during the last two or three years, is no doubt superior to Murdock's. In it a return is made to the use. of wheels with numerous teeth (thirty-one in wheels twenty inches diameter), for which epicycloidal profiles are