382 KINEMATICS OF MACHINERY.
is here complete, crank, coupler, lever, and frame all appearing in their ordinary forms outside the chamber, d is made the chamber and a the piston, while a piece connected with the lever c remains always in contact with the latter. The contact here is made by forming the end of this piece as a portion of a cylinder having its axis at 3. This machine has been constructed upon a large scale and used as a ventilator in mines. It is the only one of those represented in the last six figures which can really be called practical, for it presents no special constructive difficulties, and with the small pressures necessary in a mine ventilator there should be no difficulty in making the joints sufficiently tight.
87.
Chamber-crank Trains from the Double -crank. Plate XXVL, Figs. 1 and 2, and Plate XXVII.
The double-crank (CQ a has been several times used in chamber- gear ; I illustrate here five cases of its employment.
Fig. 3, PL XXVI. represents a pump constructed by Heppel, (Switzerland).* It is a combination of four double-cranks. The train of thought which has led up to it may have been somewhat similar to that which produced the machine, Fig. 4. PL XXI. The fixed link a is again the chamber, and one of the turning cranks d the piston, while the second turning link I here made in the form of a disc, having 2 for its centre, and connected by the link c with the piston allows of the alternate increase and decrease of the velocity of the latter.
Lemielle's ventilator, | Fig. 4, PL XXVI., which is frequently used, is a machine very similar to the last. Here a is again the chamber, but c is made the piston instead of d, and the crank 6 is formed as a drum of suitable dimensions. Very much the same may be said of Lemielle's ventilator as of Cooke's ; it has been constructed upon a large scale, and has found many friends in Belgium and in England.
- Propagation IndustrielU, vol. iv., 1869, p. 85. French patent dated 185o.
t Weisbach, Mechanik, vol. iii., part 2, p. 1118 (where a two-armed "piston- wheel" of Lemielle's is described); Dingier, Polytech. Journal, vol. 150; Civil Engineer and Architect's Journal, Sept. 1S58 ; Civil Ingenieur, i., 1854, p. 83.
