Page:The Kinematics of Machinery.djvu/380

 358 KINEMATICS OF MACHINERY.

trunnion valves in a not altogether unpractical way. I may only mention that this has actually been done in a machine intended either for a steam-engine or a pump, patented in England by Herr E. Jelowicki * in 1836.

No alteration of principle, and very little of detail, is involved in placing the pin 3 below the cylinder as in Fig. 3, PI. XVI., instead of opposite its centre as in Fig. 2. This arrangement is adopted in the steam-engine of Alban, Farcot, and others, as also in Sir-W. Armstrong's well-known hydraulic engines, &c.

The fixed link may be used as the chamber instead of one of the moving ones. In order to show this, and so to generalise somewhat the solution of the problem before us, I add in Fig. 1, PI. XVII. a construction which might be used as a pump, and in which the link c, the "cylinder" of the last figure, is made the piston. It swings to and fro from the pin 3 in the chamber I. The arrangement cannot pretend to any great practical value, although pumps have been made which are not at all unlike it, compare, e.g., Fig. 1 in PL XXV.

The steam-engine of Simpson and Shipton,-)- shown schematically in Fig. 2, PI. XVII., is a more interesting example than the last. A special test of it was made in 1848, which ostensibly proved that it really possessed the advantages claimed for it. Few illustrations, however, show more distinctly than this, on the one hand, how the feeling of interest excited by a novelty may lead even able engineers to see more in it than actually exists there, and, on the other hand, how indistinct and confused our kinematic notions have hitherto been. The inventors themselves, as well as their interpreters, appear completely perplexed in the attempt to analyse the motions going on before them. Ordinary terms will not suffice them for this purpose ; in describing the piston a and its motion they speak of an " eccentric revolving in its own diameter." An " eccentric " geometrical fiction, certainly ! Revolving in its own diameter! That this quasi-explanation consisted simply of words without meaning remained unnoticed, as did other matters in which there was an equally suspicious indis- tinctness of expression. They remained unnoticed simply because

t Johnson, Imperial Cyclopaedia, Description of plates, p. 29 ; also Newton, as above, vol. xxxvii. (1850), p. 207.
 * Newton, London Journal of Arts, etc. Conjoined series, vol. ix. (1837), p. 34.