378 KINEMA TICS OF MA CHINEE Y.
difficulties connected with it ; nor does the first machine, although in it the use of lower pairing allows the joints to be made steam- tight without difficulty, offer any practical advantages.
86.
Chamber-crank Trains from the Lever-crank. Plates XXV. and XXVI, Figs. 1 and 2.
The quadric crank-chain ( C" 4 ') has also been used in many ways as a prime-mover or pump, by forming some pair of its links into chamber and piston. Our figures represent in the first place several machines formed from the lever-crank ( (7 4 ') d .
Fig. 1, PL XXV. shows a mechanism which has been used by Bramah as a pump,* and by Morgan ( (1830) and then by Ericsson J as a steam-engine. The lever c is in each of the three cases formed as the piston, the frame d as the chamber. The motion of the piston is therefore an oscillation about the axis 4. If used as a pump its special formula is (C).
Instead of making the piston form a single sector only, two or more sectors may be employed for the purpose. Gray, in the arrangement shown in Fig. 2, used sectors which had for their outer surface spherical zones, the chamber being made part of a corresponding hollow sphere, and on this account he called his machine a spherical steam-engine. This form does not appear to possess any special advantage whatever. Thompson,|| who used two of his mechanisms as a coupled engine, used the links c and
- Laboulaye, Cinematique, 1864, p. 776.
t Propagation Industrielle, vol. iii., 1868, p. 151.
J Johnson, Imperial Cyclopaedia, Ericsson's semi-cylindrical marine engine, Description of the plates, p. 3. See also Bourne's Modern Examples of Steam, etc. Engines, where Ericsson's engines of the Dictator are illustrated by plates of which the excellence is worthy of a better subject. Root has also proposed a "double quadrant " engine in which the two pistons swing upon different centres in one chamber, which the crank shaft crosses between them. See Spon's Dictionary of Engineering, p. 2444.
Genie Industriel, vol. xii., 1856, p. 15. See also vol. xviii., p. 317; and Schweizerische Polytechn. Zeitschrift, vol. i., 1856, p. 140.
il Newton, London Journal of Arts, &c. Conjoined Series, iii., 1834. p. 125.
