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MARINE ENGINES. 391
In nearly all steam-vessels which have been built for
the merchant service recently, and in some naval vessels,
the compound engine has been adopted. Figs. 137 and 138
represent the usual form of this engine. Here A A, B B
are the small and the large, or the high-pressure and the
low-pressure cylinders respectively. 00 are the valve-
chests. G G is the condenser, which is invariably a sur-
face-condenser. The condensing water is sometimes di-
rected around the tubes contained within the casing, G G,
while the steam is exhansted around them and among them,
FIG. 138. Compound Marine Engine. Front Elevation and Section.
