Page:The Kinematics of Machinery.djvu/372

 350 KINEMATICS OF MACHINERY.

example. If no expansion were required only such valve-gear would be wanted as would suffice to prevent escape of steam in the lowest position of the coupler, where (as in Pattison's machine) the piston itself does not hinder communication between the two ports.

Plate XV. 2 represents a second of Lamb's machines, in which two similar mechanisms are united, one being placed within the other. The pistons \ and 1 2 act quite independently, they are two couplers of unequal length driving a common crank. The arrows indicating the motion of the steam as well as the ports for the inner chamber are omitted in the figure for simplicity's sake. Mr. Lamb insists most strongly that even more than two of the annular chambers and their ring-shaped pistons should be used together, intending that the second and following chambers should serve for the expansion of the steam. As the available chamber capacity both inside and outside the piston is filled and emptied once in each revolution, the machine may be considered double-acting.

Fig. 3. PL XV, shows a form of rotary steam-engine which has very frequently been proposed, by Bahrens (Koln) in 1847, by D. Napier in 1851, who patented it with certain improvements,* and then by Bompard (Piedmont) who re-invented it in 1867. f Our figure represents a double application of the train (C" 3 'P- L ) d with the link a as piston and d as chamber. The link 5 serves merely as a means for obtaining a tight joint, as a link of the chain it is itself incompletely closed. Ib still consists indeed of two cylinders or portions of two cylinders, one described about the axis of 2, and one about the axis of 3 ; but its half-moon-shaped profile is not such as will give a constrained pairing either with a or with c. The kinematic closure is here therefore brought about through the block c, but for this purpose some auxiliary arrangement has to be employed on account of the incompleteness of b. The formula therefore must be so constructed as to express the incompleteness both of I and of c. It may therefore be written as follows; indicating the double application of the same chain by the factor 2 outside the brace :

t Genie Industrie!, vol. xxxiv., 1867, p. 179.
 * Repertory of Patent Inventions, vol. xx., 1852, p. 307.