424 KINEMA TICS OF MA CHINEE Y.
practically. In 1830 Revillion obtained a patent in France* for a screw-wheel chamber-train. Such a mechanism is shown in Fig. 2, PL XXXVII., in a form which differs somewhat from that of Eevillion ; it is that which I have used for the model in my collec- tion of kinematic models. The wheels a and I are normal screws of equal pitch and opposite " hand " ; their axes are connected by the equal spur-wheels & x and \ ; the frame c forms the chamber. The outer surfaces of the threads revolve in (lower) contact with the chamber, the screws work together with higher pairing at Jcl, mn, op, etc. I have given them at qr and st such a sectional profile that the outer edges of each thread touch throughout the sides of the threads between which it is working (see just above the letters m n), which has not been done in any former machines of the kind. The profiles of the cross sections of the threads are envelopes of the helix. The screw cutting lathe makes the accurate construction of these profiles by no means very difficult. The fluid fills the spaces between the threads or teeth, and is pushed forward by the latter just as in the Pappenheim machine. One of these spaces is, for instance, that included between the chamber on the one side andm% and Jcl on the other, which is separated from the rest of the chamber by the contact at qr and s t and at the similar positions on each side of m n. The screw- wheel chamber gear can hardly be said to have any practical importance; I do not think it necessary therefore to consider here any of the other attempts to adapt it to the purposes of a steam-engine or a pump.
103. Other Simple Chamber-wheel Trains.
The various forms in which the simple chamber-wheel gear can be used have by no means been exhausted by the illustrations we have given, although these include the best known and more important of them. We have seen both equal and unequal 'spur- wheels used, as well as cylindric screw-wheels, and a suggestion ( 101) of a pair of bevel-wheels. In this last direction more has been attempted. Herr Liidecke (Dransfeld, near Gottingen) among others, has constructed a practically worthless chamber-
- Propagation Industrielle, vol. iii., 1868, p. 151,
