This arrangement was patented by Mr. Marc Brunei in 1822, and he employed an engine on this plan for pumping in the great subterraneous work of the Tunnel under the Thames. It has likewise been adapted in several steam boats. The chief improvement consists of an arrangement of the working cylinders, by which the connecting rods of two engines are made to give motion to the same crank. The annexed figure, which represents an elevation of the engine, will afford a correct idea of it. At aa is a strong triangular frame of cast-iron: within are fixed the two cylinders b b. These cylinders are inclined towards each other, so as to form an angle of 102°, which angle Mr. Brunei considers to be preferable to any other for imparting a rotatory motion to the crank by the alternating action of the piston-rods; cc are the piston-rods; dd the connecting rods attached to the crank e, which gives motion to the paddle shaft. The piston-rods are supported upon rollers, running upon guide plates to preserve their parallel motion during the stroke. The steam is received from the boilers into the small cylinders g g, and by the action of the pistons therein is alternately admitted into one end of the working cylinders, and a passage opened for its escape at the other.
The action of the piston is regulated by the eccentrics placed on the paddle shaft, as shown in Fig. 2. These eccentrics give motion to the rods h h, which, by the intermediate levers i i, operate upon the pistons in the small cylinder. This arrangement, it will be seen, is better suited to high-pressure engines than to condensing ones, as it affords no convenient mode of working the air-pump. In a French Post-office packet, on the Dover Station, the engines were somewhat similarly arranged; the two engines impelling one crank: but the cylinders were on the oscillating principle.