the whole too complicated and heavy for small vessels, preventing, at
the same time, the application of surface condensation. In the engines
of the Spanish gunboats, of which we annex an illustration from
_Engineering_, the designer, Captain Ericsson, has overcome these
objections by introducing a surface condenser, which, while it performs
the function of condensing the steam to be returned to the boiler in the
form of fresh water, serves as the principal support of the engines,
dispensing entirely with the usual framework. Besides this expedient,
each pair of cylinders have their slide frames for guiding the movements
of the piston rods cast in one piece. Altogether the combination, is
such that the total weight and space occupied by these novel twin screw
engines do not exceed the ordinary single screw engines of equal
power. Several improvements connected with the working gear have been
introduced.

[Illustration: ENGINES OF THE TWIN SCREW SPANISH GUNBOATS]

The outer bearings of the propeller shafts, always difficult to regulate
and keep in order on the twin screw system, are selfadjusting and
accommodate themselves to every change of the direction of the shafts.
This is effected by their being spherical externally, and resting in
corresponding cavities in the stern braces or hangers. The spring
bearings for supporting the middle of the shafts are also arranged on a
similar self-adjusting principle.

The thrust bearing is of peculiar construction, the arrangement being
such that the bearing surfaces remain in perfect contact however much
the shaft may be out of line. The reversing gear likewise is quite
peculiar, insuring complete control over the movement of the two
propellers under all circumstances. It is claimed that these engines are