384 KINEMATICS OF MACHINERY.
Fig. 1, PL XXVII. represents another primitive pump which comes to us from Ramelli.* It is a combination of three mechanisms of the class under consideration, and might be looked at (apart from its date) as formed by reduction from Lemielle's wheel. The guiding crank d, namely, is omitted from the chain, and also the higher pairing which should replace it, so that the piston c is force- closed only against the chamber. Its general formula, is therefore [MATH] The relation between this machine and that of Lemielle forms an interesting example of the course which we described in Chapter VI as that taken by machine development, the newer form of Lemielle is simply the kinematic completion of the older one of Ramelli.
In Fig. 2, PL XXVII., we have a machine which is an adaptation of Ramelli's pump to the purposes of a steam-engine, it is another result of the unwearying activity of Lord Cochrane. The link d is again omitted, and c force-closed. The machine is altogether very incomplete.
Fig. 3, PL XXVIL, represents another, and much less incomplete form of rotary steam-engine founded upon the mechanism (MATH). It is the invention of Rösky (Elbing) and is known to me only by description, The chain is used singly only, so that a separate valve has to be employed to prevent the steam from passing through the chamber when c is at the lower part of it. The link d is held against the wall of the chamber by force-closure. Its formula is therefore, c being the driving link, (MATH), and for the chambering (V±) = c, a. 50
88. Chamber Trains from Conic Crank Mechanisms.
Among the numerous steam-engines and pumps which we have now described and analysed there are many which it has been possible either to explain or to describe by the older methods only with difficulty, and the nature of which, therefore, has remained indistinctly understood by very many mechanicians. Besides these, however, there exists a machine, or rather a small series of machines,
- Ramelli, Arteficiose Machine, 1588, p. 60.